Display Device and Electronic Device

ABSTRACT

A display device including a peripheral circuit portion with high operation stability. The display device includes a first substrate and a second substrate. A first insulating layer is on a first plane of the first substrate, and a second insulating layer is on a first plane of the second substrate. An area of the first plane of the first substrate is the same as an area of the first plane of the second substrate. The first plane of the first substrate and the first plane of the second substrate face each other. A bonding layer is between the first insulating layer and the second insulating layer. A protection film is in contact with the first substrate, the first insulating layer, the bonding layer, the second insulating layer, and the second substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and an electronicdevice.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of the invention disclosed inthis specification and the like relates to an object, a method, or amanufacturing method. In addition, one embodiment of the presentinvention relates to a process, a machine, manufacture, or a compositionof matter. Specifically, examples of the technical field of oneembodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, an input device, aninput/output device, a method for driving any of them, and a method formanufacturing any of them.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A semiconductor element such as a transistor, asemiconductor circuit, an arithmetic device, and a memory device areeach an embodiment of a semiconductor device. An imaging device, adisplay device, a liquid crystal display device, a light-emittingdevice, an electro-optical device, a power generation device (includinga thin film solar cell, an organic thin film solar cell, and the like),and an electronic device may each include a semiconductor device.

2. Description of the Related Art

Displays including thin film transistors have been widely spread andindispensable to our life. In addition, these displays are thin andlightweight, and have been necessary for portable information terminals.

Furthermore, display devices in which a display region (a pixel portion)and a peripheral circuit (a driver portion) are provided in the samesubstrate have been widely used. For example, Patent Document 1discloses a technique of using oxide semiconductor transistors in thedisplay region and the peripheral circuit. When the display region andthe peripheral circuit are formed simultaneously, the manufacturing costcan be reduced.

REFERENCE Patent Document [Patent Document 1] Japanese Published PatentApplication No. 2007-123861 SUMMARY OF THE INVENTION

A display device is required to have as large a display region aspossible on a side viewed by a viewer (a display surface side). In orderto enlarge the display region, a frame, which extends in a region fromthe edge of the display region to the edge of a substrate, needs to beas narrow as possible.

A driver circuit around the display region is positioned in such a frameregion. When the display region is enlarged and the frame is narrowed,the driver circuit is disposed closer to the edge of the substrate.Therefore, atmospheric components might enter and lower characteristicsof a transistor in the driver circuit, which might cause unstablecircuit operation.

An object of one embodiment of the present invention is to provide adisplay device including a peripheral circuit portion with highoperation stability.

Another object of one embodiment of the present invention is to providea display device with a narrow frame.

Another object of one embodiment of the present invention is to providea lightweight display device.

Another object of one embodiment of the present invention is to providea high-definition display device.

Another object of one embodiment of the present invention is to providea highly reliable display device.

Another object of one embodiment of the present invention is to providea large-area display device.

Another object of one embodiment of the present invention is to providea low-power display device.

Another object of one embodiment of the present invention is to providea novel display device or the like.

Another object of one embodiment of the present invention is to providea method for manufacturing the display device.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention is a display device including afirst substrate and a second substrate. A first insulating layer is on afirst plane of the first substrate. A second insulating layer is on afirst plane of the second substrate. An area of the first plane of thefirst substrate is the same as an area of the first plane of the secondsubstrate. The first plane of the first substrate and the first plane ofthe second substrate face each other. A bonding layer is between thefirst insulating layer and the second insulating layer. A protectionfilm is in contact with the first substrate, the first insulating layer,the bonding layer, the second insulating layer, and the secondsubstrate.

One embodiment of the present invention is a display device including afirst substrate and a second substrate. A first insulating layer is on afirst plane of the first substrate. A second insulating layer is on afirst plane of the second substrate. An area of the first plane of thesecond substrate is smaller than an area of the first plane of the firstsubstrate. The first plane of the first substrate and the first plane ofthe second substrate face each other. A bonding layer is between thefirst insulating layer and the second insulating layer. A protectionfilm is in contact with the first substrate, the first insulating layer,the bonding layer, the second insulating layer, and the secondsubstrate.

A transistor, a capacitor, a display element, a light-blocking layer, acoloring layer, and a spacer can be included between the first plane ofthe first substrate and the first plane of the second substrate.

For the protection film, an oxide, a nitride, or a metal can be used.

For the protection film, aluminum oxide, hafnium oxide, zirconium oxide,titanium oxide, zinc oxide, indium oxide, tin oxide, indium tin oxide,tantalum oxide, silicon oxide, manganese oxide, nickel oxide, erbiumoxide, cobalt oxide, tellurium oxide, barium titanate, titanium nitride,tantalum nitride, aluminum nitride, tungsten nitride, cobalt nitride,silicon nitride, manganese nitride, hafnium nitride, ruthenium,platinum, nickel, cobalt, manganese, or copper can be used.

The protection film can contain fluorine, carbon, or hydrogen.

The concentration of fluorine in the protection film is preferablygreater than or equal to 1×10¹⁸ atoms/cm³ and less than 1×10²²atoms/cm³.

The concentration of carbon in the protection film is preferably greaterthan or equal to 1×10¹⁷ atoms/cm³ and less than 1×10²² atoms/cm³.

The concentration of hydrogen in the protection film is preferablygreater than or equal to 1×10¹⁹ atoms/cm³ and less than 1×10²²atoms/cm³.

Any of the aforementioned display devices can include a liquid crystalelement.

Any of the aforementioned display devices can include an organic ELelement.

Any of the aforementioned display devices can be combined with amicrophone and a speaker.

Note that other embodiments of the present invention are shown below inthe description of Embodiments and the drawings.

One embodiment of the present invention can provide a display device inwhich a peripheral circuit portion has high operation stability.

Another embodiment of the present invention can provide a display devicewith a narrow frame.

Another embodiment of the present invention can provide a lightweightdisplay device.

Another embodiment of the present invention can provide ahigh-definition display device.

Another embodiment of the present invention can provide a highlyreliable display device.

Another embodiment of the present invention can provide a large-areadisplay device.

Another embodiment of the present invention can provide a low-powerdisplay device.

Another embodiment of the present invention can provide a novel displaydevice or the like.

Alternatively, a method for manufacturing the display device can beprovided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are a top view and cross-sectional views illustrating adisplay device of one embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views each illustrating a displaydevice of one embodiment of the present invention.

FIGS. 3A to 3C are cross-sectional views illustrating a method formanufacturing a display device of one embodiment of the presentinvention.

FIGS. 4A and 4B are cross-sectional views each illustrating a displaydevice of one embodiment of the present invention.

FIGS. 5A to 5D are a top view and cross-sectional views eachillustrating a display device of one embodiment of the presentinvention.

FIGS. 6A to 6E are cross-sectional views each illustrating a displaydevice of one embodiment of the present invention.

FIGS. 7A to 7D are cross-sectional views illustrating a method formanufacturing a display device of one embodiment of the presentinvention.

FIGS. 8A to 8D are schematic cross-sectional views illustrating a filmformation principle.

FIG. 9A is a schematic cross-sectional view of a deposition apparatusand FIG. 9B is a schematic top view of a manufacturing apparatusprovided with the deposition apparatus.

FIGS. 10A and 10B are schematic cross-sectional views of depositionapparatuses.

FIGS. 11A and 11B are a top view and a cross-sectional view illustratinga display device of one embodiment of the present invention.

FIG. 12 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 13 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 14 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 15 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 16 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 17 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 18 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 19 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 20 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 21 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 22 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 23 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 24 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 25 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 26 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 27 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 28 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 29 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 30 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 31 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIG. 32 is a cross-sectional view illustrating a display device of oneembodiment of the present invention.

FIGS. 33A and 33B are cross-sectional views each illustrating atransistor of one embodiment of the present invention.

FIGS. 34A and 34B are cross-sectional views each illustrating atransistor of one embodiment of the present invention.

FIGS. 35A to 35C are a top view and cross-sectional views illustrating atransistor of one embodiment of the present invention.

FIGS. 36A to 36C are a top view and circuit diagrams illustrating adisplay device of one embodiment of the present invention.

FIG. 37 is a top view illustrating positional relations of a pixel, atransistor, and wirings of a touch sensor.

FIGS. 38A to 38D are top views each illustrating an input device of oneembodiment of the present invention.

FIGS. 39A to 39D are top views each illustrating an input device of oneembodiment of the present invention.

FIGS. 40A to 40C are top views each illustrating an input device of oneembodiment of the present invention.

FIGS. 41A to 41F are top views each illustrating an input device of oneembodiment of the present invention.

FIGS. 42A and 42B are circuit diagrams illustrating an input device ofone embodiment of the present invention.

FIGS. 43A and 43B are circuit diagrams illustrating an input device ofone embodiment of the present invention.

FIGS. 44A to 44D illustrate a deposition method of a CAAC-OS.

FIG. 45 illustrates a crystal structure of InMZnO₄.

FIGS. 46A to 46E illustrate a deposition method of a CAAC-OS.

FIGS. 47A to 47C illustrate a deposition method of a CAAC-OS.

FIG. 48 illustrates a deposition method of an nc-OS.

FIG. 49 is a top view illustrating a display module to which asemiconductor device of one embodiment of the present invention isapplied.

FIGS. 50A to 50F each illustrate an electronic device of one embodimentof the present invention.

FIGS. 51A to 51D each illustrate an electronic device of one embodimentof the present invention.

FIG. 52 shows results of Ca tests with/without a protection film formedby an ALD method.

FIG. 53 shows measurement results of voltage holding ratios of samplesthat use positive-type liquid crystal and one embodiment of the presentinvention.

FIG. 54 shows measurement results of voltage holding ratios of samplesthat use negative-type liquid crystal and one embodiment of the presentinvention.

FIG. 55 shows display of a display device manufactured using oneembodiment of the present invention.

FIG. 56A is a schematic cross-sectional view of a display panel, andFIG. 56B is a schematic cross-sectional view of a region observed bySEM.

FIG. 57A is a cross-sectional SEM image of a side surface portion of adisplay panel, and FIGS. 57B and 57C show mapping analysis resultsthereof by EDX.

FIGS. 58A and 58C are cross-sectional SEM images of a side surfaceportion of a display panel, and FIG. 58B shows a mapping analysis resultthereof by EDX.

FIG. 59 shows SIMS analysis results of aluminum oxide films formed by anALD method or a sputtering method.

FIG. 60A is a top view of a sample used for light transmittancemeasurement and FIGS. 60B and 60C each illustrate a method for driving adisplay.

FIG. 61 shows voltage-light transmittance characteristics in gray level.

FIGS. 62A and 62B show the light transmittance of samples subjected to apreservation test at a temperature of 60° C. and a humidity of 90%.

FIG. 63 shows evaluation results of the density of the aluminum oxidefilms.

FIG. 64 shows measurement results of Ca tests of samples with/without aprotection film formed by an ALD method.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below. Note that in the structures of the inventiondescribed below, the same portions or portions having similar functionsare denoted by the same reference numerals in different drawings, anddescription of such portions is not repeated.

<Notes on the Description for Drawings>

In this specification, terms for describing arrangement, such as “over”and “under”, are used for convenience to describe a positional relationbetween components with reference to drawings. Furthermore, thepositional relation between components is changed as appropriate inaccordance with a direction in which each component is described. Thus,there is no limitation on terms used in this specification, anddescription can be made appropriately depending on the situation.

The term “over” or “below” does not necessarily mean that a component isplaced directly on or directly below and directly in contact withanother component. For example, the expression “electrode B overinsulating layer A” does not necessarily mean that the electrode B is onand in direct contact with the insulating layer A and can mean the casewhere another component is provided between the insulating layer A andthe electrode B.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.The term “substantially parallel” indicates that the angle formedbetween two straight lines is greater than or equal to −30° and lessthan or equal to 30°. The tetra “perpendicular” indicates that the angleformed between two straight lines is greater than or equal to 80° andless than or equal to 100°, and accordingly includes the case where theangle is greater than or equal to 85° and less than or equal to 95°. Theterm “substantially perpendicular” indicates that the angle formedbetween two straight lines is greater than or equal to 60° and less thanor equal to 120°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

In drawings, the size, the layer thickness, or the region is determinedarbitrarily for description convenience. Therefore, the size, the layerthickness, or the region is not limited to the illustrated scale. Notethat the drawings are schematically shown for clarity, and embodimentsof the present invention are not limited to shapes or values shown inthe drawings.

In drawings such as plan views (also referred to as layout views) andperspective views, some of components might not be illustrated forclarity of the drawings.

The expression “being the same” may refer to having the same area orhaving the same shape. In addition, the expression “being the same”include a case of “being substantially the same” because a manufacturingprocess might cause some differences.

<Notes on Expressions that can be Rephrased>

In this specification and the like, in describing connections of atransistor, expressions “one of a source and a drain” (or a firstelectrode or a first terminal) and “the other of the source and thedrain” (or a second electrode or a second terminal) are used. This isbecause a source and a drain of a transistor are interchangeabledepending on the structure, operation conditions, or the like of thetransistor. Note that the source or the drain of the transistor can alsobe referred to as a source (or drain) terminal, a source (or drain)electrode, or the like as appropriate depending on the situation.

In addition, in this specification and the like, the term such as an“electrode” or a “wiring” does not limit a function of the component.For example, an “electrode” is used as part of a “wiring” in some cases,and vice versa. Further, the term “electrode” or “wiring” can also meana combination of a plurality of “electrodes” and “wirings” formed in anintegrated manner.

In this specification and the like, a transistor is an element having atleast three terminals: a gate, a drain, and a source. The transistor hasa channel region between the drain (a drain terminal, a drain region, ora drain electrode) and the source (a source terminal, a source region,or a source electrode), and current can flow through the drain, thechannel region, and the source.

Since the source and the drain of the transistor change depending on thestructure, operating conditions, and the like of the transistor, it isdifficult to define which is a source or a drain. Thus, a portion thatfunctions as a source or a portion is not referred to as a source or adrain in some cases. In that case, one of the source and the drain mightbe referred to as a first electrode, and the other of the source and thedrain might be referred to as a second electrode.

In this specification, ordinal numbers such as first, second, and thirdare used to avoid confusion among components, and thus do not limit thenumber of the components.

In this specification and the like, a structure in which a flexibleprinted circuit (FPC), a tape carrier package (TCP), or the like isattached to a substrate of a display panel, or a structure in which anintegrated circuit (IC) is directly mounted on a substrate by a chip onglass (COG) method is referred to as a display device in some cases.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film” insome cases. In addition, the term “insulating film” can be changed intothe term “insulating layer” in some cases.

<Notes on Definitions of Terms>

The following are definitions of the terms that are not mentioned in theabove embodiments.

<<Connection>>

In this specification, when it is described that “A and B are connectedto each other”, the case where A and B are electrically connected toeach other is included in addition to the case where A and B aredirectly connected to each other. Here, the expression “A and B areelectrically connected” means the case where electric signals can betransmitted and received between A and B when an object having anyelectric action exists between A and B.

Note that these expressions are examples and there is no limitation onthe expressions. Here, X, Y, Z1, and Z2 each denote an object (e.g., adevice, an element, a circuit, a wiring, an electrode, a terminal, aconductive film, and a layer).

Note that a content (or may be part of the content) described in oneembodiment may be applied to, combined with, or replaced by a differentcontent (or may be part of the different content) described in theembodiment and/or a content (or may be part of the content) described inone or a plurality of different embodiments.

Note that in each embodiment, a content described in the embodiment is acontent described with reference to a variety of diagrams or a contentdescribed with a text described in this specification.

Note that by combining a diagram (or may be part of the diagram)illustrated in one embodiment with another part of the diagram, adifferent diagram (or may be part of the different diagram) illustratedin the embodiment, and/or a diagram (or may be part of the diagram)illustrated in one or a plurality of different embodiments, much morediagrams can be formed.

Embodiment 1

In this embodiment, structural examples of a display panel aredescribed.

<Protection of Substrate Surface Portion and Side Surface Portion byProtection Film 23>

FIG. 1A is a top view of a display device, and FIGS. 1B and 1C arecross-sectional views thereof. A display device 10 in FIG. 1A includesan FPC 42 and a display panel 20 including a display region 21 and aperipheral circuit 22. In one embodiment of the present invention, aprotection film 23 is uniformly formed over the display panel 20. Theprotection film 23 is preferably formed by an atomic layer deposition(ALD) method. Note that a protection film such as the protection film 23has a function of, for example, protecting a display element and atransistor, and in some cases has another function of, for example,adding one or more kinds of components to a display element or atransistor. For this reason, the protection film such as the protectionfilm 23 is simply called a film in some cases. For example, theprotection film such as the protection film 23 is called a first film, asecond film, or the like in some cases.

FIG. 1B is a cross-sectional view of an edge of a substrate of thedisplay panel taken along the dashed line A1-A2 in FIG. 1A. A3 indicatesan edge of a region including a bonding layer 370, and A4 indicates anedge of the peripheral circuit. In the display panel, a transistor, acapacitor, a display element, and the like are formed. The display panelincludes, at the edge of the substrate, a substrate 100, a substrate 300an insulating layer 130, an insulating layer 131, an insulating layer170, an insulating layer 180, an insulating layer 181, an insulatinglayer 182, a light-blocking layer 18, an insulating layer 330, a spacer240, and the bonding layer 370 which are covered with the protectionfilm 23. In FIG. 1B, the substrate 100 and the substrate 300 overlapeach other and can have substantially the same area. Thanks to havingthe same area of the substrates, alignment controllability at the timeof bonding the substrates can be improved.

The thickness of the protection film 23 is greater than or equal to 3 nmand less than or equal to 200 nm, preferably greater than or equal to 5nm and less than 150 nm. With a thickness in the above range, a barrierproperty can be improved and atmospheric components can be preventedfrom entering the inside of the display panel.

Alternatively, the concentration of hydrogen in the protection film 23is greater than or equal to 1×10¹⁹ atoms/cm³ and less than 1×10²²atoms/cm³, preferably greater than or equal to 1×10¹⁹ atoms/cm³ and lessthan 1×10²¹ atoms/cm³. In the case where the protection film 23 containsmuch hydrogen, hydrogen might enter the display panel from theprotection film 23 and thus characteristics of the peripheral circuitmight deteriorate. Therefore, by setting the concentration of hydrogenin the protection film in the above range, the protection film 23 canhave high purity, entry of hydrogen from the protection film to thedisplay panel can be prevented, and the operation stability andreliability of the peripheral circuit can be improved.

Alternatively, the concentration of carbon in the protection film 23 isgreater than or equal to 1×10¹⁷ atoms/cm³ and less than 1×10²²atoms/cm³, preferably greater than or equal to 1×10¹⁷ atoms/cm³ and lessthan 1×10²¹ atoms/cm³, more preferably greater than or equal to 1×10¹⁷atoms/cm³ and less than 1×10²⁰ atoms/cm³. By having a concentration ofcarbon within the above range, the protection film 23 can be denser andhave a higher barrier property.

Alternatively, the concentration of fluorine in the protection film 23is greater than or equal to 1×10¹⁸ atoms/cm³ and less than 1×10²²atoms/cm³, preferably greater than or equal to 1×10¹⁸ atoms/cm³ and lessthan 1×10²¹ atoms/cm³. By having a concentration of fluorine within theabove range, the protection film 23 can be denser and have a higherbarrier property.

<Method for Forming Protection Film 23 of Display Panel by ALD Method>

A method for forming the protection film 23 of the display panel by anALD method is described with reference to FIGS. 3A to 3C.

A transistor, a capacitor, part of a display element, and the like areprovided over the substrate 100, whereby a region 11 is formed. Alight-blocking layer, a coloring layer, an insulating layer, part of thedisplay element, and the like are provided over the substrate 300,whereby a region 12 is formed (see FIG. 3A).

Next, the region 11 of the substrate 100 and the region 12 of thesubstrate 300 are disposed to face each other, and the substrate 100 andthe substrate 300 are bonded with the bonding layer 370, whereby thedisplay panel 20 can be formed (see FIG. 3B).

The temperature for forming the protection film 23 by an ALD method canbe greater than or equal to room temperature and less than 200° C.,preferably greater than or equal to 50° C. and less than 150° C.

By an ALD method, the protection film can be deposited extremelyuniformly on a surface on which the protection film is deposited. Byusing an ALD method, for example, aluminum oxide, hafnium oxide,zirconium oxide, titanium oxide, zinc oxide, indium oxide, tin oxide,indium tin oxide (ITO), tantalum oxide, silicon oxide, manganese oxide,nickel oxide, erbium oxide, cobalt oxide, tellurium oxide, bariumtitanate, titanium nitride, tantalum nitride, aluminum nitride, tungstennitride, cobalt nitride, silicon nitride, manganese nitride, hafniumnitride, and the like can be deposited as the protection film.Furthermore, the protection film is not limited to an insulating film,and a conductive film may also be deposited. For example, ruthenium,platinum, nickel, cobalt, manganese, copper, and the like can bedeposited.

Furthermore, a portion electrically connected to the FPC 42 or the likeis preferably masked so that the protection film 23 is not deposited onthe portion. For the masking, an organic film, an inorganic film, ametal, or the like can be used. For example, an oxide insulating filmsuch as silicon oxide, silicon oxynitride, gallium oxide, galliumoxynitride, yttrium oxide, yttrium oxynitride, hafnium oxide, or hafniumoxynitride, a nitride insulating film such as silicon nitride oraluminum nitride, or an organic material such as a photoresist, apolyimide resin, an acrylic resin, a polyimide amide resin, abenzocyclobutene resin, a polyamide resin, or an epoxy resin can beused. In the case where any of these films is used as a mask, the maskcan be removed after the protection film 23 is deposited.

Furthermore, a region on which the protection film is deposited may bemasked with a metal mask by an ALD method. The metal mask can be formedusing a metal element selected from iron, chromium, nickel, cobalt,tungsten, molybdenum, aluminum, copper, tantalum, and titanium, an alloyincluding any of the metal elements, an alloy including any of the metalelements in combination, or the like. The metal mask can be positionedin the proximity of or in contact with the display panel.

A dense film can be formed by an ALD method. When the protection film 23is deposited on the side surface portion of the display panel by an ALDmethod, entry of external components such as moisture can be inhibited.As a result, a change in transistor characteristics can be inhibited andthe operation of the peripheral circuit can be stable. Moreover, theframe size can be reduced; thus, the pixel region can be enlarged andthe definition of the display device can be increased.

With the protection film 23, even if a distance A1-A4 between an edge ofthe peripheral circuit 22 and the edge of the substrate is narrowed, thestable transistor characteristics, that is, the operation stability ofthe peripheral circuit, can be obtained because of a high barrierproperty of the protection film 23; thus, the frame of the display panelcan be narrowed. For example, the distance A1-A4 between the edge of theperipheral circuit 22 and the edge of the substrate (a portion cut bythe panel processing) can be 300 μm or shorter, preferably 200 μm orshorter. Alternatively, the edge of the display panel may have astructure without unevenness in shape as illustrated in FIG. 1C.

Metal components in the protection film 23 can be diffused into theinsulating layer formed on the protection film 23. For example, in thecase where the protection film 23 is formed over the insulating layer330 while being heated and the insulating layer 330 is formed of anorganic resin, the resin is softened and metal components in theprotection film 23 can be diffused into the insulating layer.

Furthermore, a resin film can be provided on an outer surface of theprotection film 23. This can disperse various pressures and thus canprevent a break of the insulating layer caused by pressureconcentration. As a result, a display device that is highly convenientor highly reliable can be provided.

<Variation 1 of Structure of Peripheral Portion of Display Panel>

FIGS. 2A and 2B show other structural examples of FIG. 1B. A regionwhere the protection film is formed can be controlled by masking. Inthis case, the protection film 23 can be deposited on a small region ona rear surface side of the display device as illustrated in FIG. 2A, orcan be prevented from being deposited on the rear surface side (a region14) as illustrated in FIG. 2B.

<Variation 2 of Structure of Peripheral Portion of Display Panel>

FIGS. 4A and 4B show another structural example of FIG. 1B. Theprotection film 23 can inhibit entry of moisture and the like and canreduce the number of insulating layers. The structures illustrated inFIGS. 4A and 4B do not include the insulating layer 182 that is used inFIGS. 1B and 1C.

<Variation 3 of Structure of Peripheral Portion of Display Panel>

FIG. 5A shows a structural example different from the structuralexamples of FIGS. 4A and 4B. FIG. 5A is a top view of the display panel20 seen from the substrate 300 side, and FIG. 5B is a cross-sectionalview taken along the dashed-dotted line A1-A2 in FIG. 5A. In FIG. 5A,some layers are omitted for easy viewing. As in FIG. 4A, the structureillustrated in FIG. 5B does not include the insulating layer 182illustrated in FIG. 1B. In FIGS. 5A and 5B, the area of a top surface ofthe substrate 300 can be smaller than the area of a top surface of thesubstrate 100. In such a case, the peripheral portion of the substrate100 is exposed when seen from the top surface side (the substrate 300side) as illustrated in FIG. 5A, and the bonding layer 370 has aninclined side surface; thus, the protection film 23 can be formed moreuniformly.

FIG. 5C shows a structural example different from the structural exampleof FIG. 5A. As illustrated in FIG. 5C, a structure in which the area ofthe top surface of the substrate 300 is smaller than the area of the topsurface of the substrate 100 and there is not unevenness between thesubstrate 300 and the substrate 100 may be employed. Alternatively, asillustrated in FIG. 5D, the protection film 23 may be hardly depositedon the surfaces of the substrate 100 and the substrate 300.

<Variation 4 of Structure of Peripheral Portion of Display Panel>

FIGS. 6A to 6E show structural examples different from the structuralexample of FIG. 1B. The protection film 23 can inhibit entry of moistureand the like and can further reduce the number of insulating layers. Thestructures in FIGS. 6A to 6E do not include the insulating layer 181 andthe insulating layer 182 that are used in FIGS. 1B and 1C. Theperipheral portion may have unevenness as in FIG. 6A or may have nounevenness as in FIG. 6B. As in FIGS. 6B and 6C, the spacer 240 may beomitted. As in FIG. 6D, the protection film 23 may be hardly depositedon the surfaces of the substrate 100 and the substrate 300. As in FIG.6E, the protection film 23 in the region 14 may be omitted.

In Embodiment 1, one embodiment of the present invention has beendescribed. Other embodiments of the present invention are described inEmbodiments 2 to 10. Note that one embodiment of the present inventionis not limited thereto. In other words, various embodiments of theinvention are described in Embodiments 1 to 10, and one embodiment ofthe present invention is not limited to a particular embodiment.Although the example where a film is formed by an ALD method isdescribed in one embodiment of the present invention, one embodiment ofthe present invention is not limited thereto. Depending on the case orthe situation, a variety of film formation methods can be employed inone embodiment of the present invention. For example, in one embodimentof the present invention, a film may be formed by at least any one of aCVD method, a plasma CVD method, an MOCVD method, a PVD method, asputtering method, an evaporation method, a spin coating method, anink-jet method, a printing method, and a coating method. Alternatively,depending on the case or the situation, a film may be formed withoutusing an ALD method in one embodiment of the present invention.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 2

In this embodiment, a method for manufacturing a plurality of displaypanels including the protection film 23 described in Embodiment 1 isdescribed.

FIGS. 7A to 7D illustrate a manufacturing method of the display panel20. In the schematic views of FIGS. 7A to 7D, a liquid crystal element80 and the adhesive layer 370 are illustrated as a display element, anda display panel can be formed by bonding an element substrate where atransistor, a capacitor, and the like are provided for the substrate 100and a counter substrate where a light-blocking layer, a coloring layer,and the like are provided for the substrate 300 to seal liquid crystal.Note that portions similar to those of the manufacturing method in FIGS.3A to 3C are omitted.

In a structure including the plurality of display panels 20 (see FIG.7A), the substrate 300 (an upper side) is cut to form a groove portion30 (see FIG. 7B). After the formation of the groove portion 30, theprotection film 23 is formed from the upper side by an ALD method (seeFIG. 7C), and the substrate 100 is cut, whereby the plurality of displaypanels can be finally manufactured (see FIG. 7D). Note that in thiscase, the formation of the protection film 23 on a rear surface of thedisplay device can be inhibited.

After the cutting, another protection film may be formed by an ALDmethod.

When the substrate 100 is divided as in FIG. 7D, a damaged region thatcontains a tiny crack (also, referred to as microcrack) is formed in afilm at/near the edge of the substrate in some cases. Specifically, whenglass is divided by scribing and pressure is applied so as toconcentrate a scribed portion, a microcrack is formed at an edge of thedivided glass in some cases. In such a case, when the protection film isformed by an ALD method, the protection film fills the microcrack in thedamaged region; thus, the protection film can cover the damaged region.Accordingly, embrittlement or a crack in the substrate or the film canbe suppressed in the following manufacturing process.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 3 <<Deposition Method>>

A deposition apparatus which can be used for forming a semiconductorlayer, an insulating layer, a conductive layer, and the like, which canbe used in one embodiment of the present invention, is described below.

<<CVD and ALD>>

In a conventional deposition apparatus utilizing a CVD method, one ormore kinds of source gases (precursors) for reaction are supplied to achamber at the same time at the time of deposition. In a depositionapparatus utilizing an ALD method, precursors for reaction aresequentially introduced into a chamber, and then the sequence of the gasintroduction is repeated. For example, two or more kinds of precursorsare sequentially supplied to the chamber by switching respectiveswitching valves (also referred to as high-speed valves). For example, afirst precursor is introduced, an inert gas (e.g., argon or nitrogen) orthe like is introduced after the introduction of the first precursor sothat the plural kinds of precursors are not mixed, and then a secondprecursor is introduced. Alternatively, the first precursor may beexhausted by vacuum evacuation instead of the introduction of the inertgas, and then the second precursor may be introduced.

FIGS. 8A to 8D show a film formation process by an ALD method. Firstprecursors 601 are adsorbed onto a substrate surface (see FIG. 8A),whereby a first monolayer is formed (see FIG. 8B). At this time, metalatoms and the like included in the precursors can be bonded to hydroxylgroups that exist at the substrate surface. The metal atoms may bebonded by alkyl groups such as methyl groups or ethyl groups. The firstmonolayer reacts with second precursors 602 introduced after the firstprecursors 601 are exhausted (see FIG. 8C), whereby a second monolayeris stacked over the first monolayer. Thus, a thin film is formed (seeFIG. 8D). For example, in the case where an oxidizer is included in thesecond precursors, the oxidizer chemically reacts with metal atomsincluded in the first precursors or an alkyl group bonded to metalatoms, whereby an oxide film can be formed.

An ALD method is a film formation method based on a surface chemicalreaction, by which precursors are adsorbed onto a surface and adsorbingis stopped by a self-terminating mechanism, whereby a layer is formed.For example, precursors such as trimethylaluminum react with hydroxylgroups (OH groups) that exist at the surface. At this time, only asurface reaction due to heating occurs; therefore, the precursors comeinto contact with the surface and metal atoms or the like in theprecursors can be adsorbed onto the surface by thermal energy. Theprecursors have characteristics of, for example, having a high vaporpressure, being thermally stable and not decomposed before beingdeposited, and being chemically adsorbed onto a substrate at a highspeed. Since the precursors are introduced in a state of a gas, when thefirst precursors and the second precursors, which are alternatelyintroduced, have enough time to be diffused, a film can be formed withgood coverage even onto a region having unevenness with a high aspectratio.

In an ALD method, the sequence of the gas introduction is repeated aplurality of times until a desired thickness is obtained, whereby a thinfilm with excellent step coverage can be formed. The thickness of thethin film can be precisely adjusted by controlling the number ofrepeating times. The deposition rate can be increased and the impurityconcentration in the film can be reduced by improving the exhaustioncapability.

An ALD method includes an ALD method using heating (thermal ALD method)and an ALD method using plasma (plasma ALD method). In the thermal ALDmethod, precursors react with each other using thermal energy, and inthe plasma ALD method, precursors react with each other in a state of aradical.

By an ALD method, an extremely thin film can be formed with highaccuracy. In addition, the coverage of an uneven surface with the filmand the film density of the film are high.

Furthermore, plasma damage is not caused by the thermal ALD method.Therefore, generation of defects in a film can be inhibited.

<<Plasma ALD>>

Alternatively, when the plasma ALD method is employed, the film can beformed at a lower temperature than when the thermal ALD method isemployed. With the plasma ALD method, for example, the film can beformed without decreasing the deposition rate even at 100° C. or lower.Moreover, in the plasma ALD method, nitrogen radicals can be formed byplasma; thus, a nitride film as well as an oxide film can be formed.

In addition, oxidizability of an oxidizer can be enhanced by the plasmaALD method. By the plasma ALD method, precursors remaining in the filmor organic components released from precursors can be reduced. Inaddition, carbon, chlorine, hydrogen, and the like in the film can bereduced. Therefore, a film with low impurity concentration can beformed.

Furthermore, in the case where a light-emitting element (such as anorganic EL element) is used as a display element, when a processtemperature is high, the deterioration of the light-emitting element maybe accelerated. Here, with the plasma ALD method, the processtemperature can be lowered; thus, the deterioration of thelight-emitting element can be inhibited.

In the case of using the plasma ALD, inductively coupled plasma (ICP) isused to generate radical species. Accordingly, plasma can be generatedat a place apart from the substrate, so that plasma damage to thesubstrate or a film on which the protection film is formed can beinhibited.

As described above, with the plasma ALD method, the process temperaturecan be lowered and the coverage of the surface can be increased ascompared with other deposition methods, and the protection film can bedeposited on the side surface portion of the substrate after the displaypanel is fabricated. Thus, entry of water from the outside can beinhibited. Therefore, the reliability of driver operation of aperipheral circuit at an edge portion of a panel is improved (thetransistor characteristics are improved), so that a stable operation canbe achieved even in the case of employing a narrow frame.

<<ALD Apparatus>>

FIG. 9A illustrates an example of a deposition apparatus utilizing anALD method. The deposition apparatus utilizing an ALD method includes adeposition chamber (chamber 1701), source material supply portions 1711a and 1711 b, high-speed valves 1712 a and 1712 b which are flow ratecontrollers, source material introduction ports 1713 a and 1713 b, asource material exhaust port 1714, and an evacuation unit 1715. Thesource material introduction ports 1713 a and 1713 b provided in thechamber 1701 are connected to the source material supply portions 1711 aand 1711 b, respectively, through supply tubes and valves. The sourcematerial exhaust port 1714 is connected to the evacuation unit 1715through an exhaust tube, a valve, and a pressure controller.

A substrate holder 1716 with a heater is provided in the chamber, and asubstrate 1700 over which a film is formed is provided over thesubstrate holder.

In the source material supply portions 1711 a and 1711 b, a precursor isformed from a solid source material or a liquid source material by usinga vaporizer, a heating unit, or the like. Alternatively, the sourcematerial supply portions 1711 a and 1711 b may supply a precursor in agas state.

Although two source material supply portions 1711 a and 1711 b areprovided as an example, the number of source material supply portions isnot limited thereto, and three or more source material supply portionsmay be provided. The high-speed valves 1712 a and 1712 b can beaccurately controlled by time, and a precursor and an inert gas aresupplied by the high-speed valves 1712 a and 1712 b. The high-speedvalves 1712 a and 1712 b are flow rate controllers for a precursor, andcan also be referred to as flow rate controllers for an inert gas.

In the deposition apparatus illustrated in FIG. 9A, a thin film isformed over a surface of the substrate 1700 in the following manner: thesubstrate 1700 is transferred to put on the substrate holder 1716, thechamber 1701 is sealed, the substrate 1700 is heated to a desiredtemperature (e.g., higher than or equal to 100° C. or higher than orequal to 150° C.) by heating the substrate holder 1716 with a heater;and supply of a precursor, evacuation with the evacuation unit 1715,supply of an inert gas, and evacuation with the evacuation unit 1715 arerepeated.

In the deposition apparatus illustrated in FIG. 9A, an insulating layerformed using an oxide (including a composite oxide) containing one ormore elements selected from hafnium, aluminum, tantalum, zirconium, andthe like can be formed by selecting a source material (e.g., a volatileorganometallic compound) used for the source material supply portions1711 a and 1711 b appropriately. Specifically, it is possible to use aninsulating layer formed using hafnium oxide, an insulating layer formedusing aluminum oxide, an insulating layer formed using hafnium silicate,or an insulating layer formed using aluminum silicate. Alternatively, athin film, e.g., a metal layer such as a tungsten layer or a titaniumlayer, or a nitride layer such as a titanium nitride layer can be formedby selecting a source material (e.g., a volatile organometalliccompound) used for the source material supply portions 1711 a and 1711 bappropriately.

For example, in the case where a hafnium oxide layer is formed by adeposition apparatus using an ALD method, two kinds of gases, i.e.,ozone (O₃) as an oxidizer and a precursor which is obtained byvaporizing liquid containing a solvent and a hafnium precursor compound(hafnium alkoxide or hafnium amide such astetrakis(dimethylamide)hafnium (TDMAH)) are used. In this case, thefirst precursor supplied from the source material supply portion 1711 ais TDMAH, and the second precursor supplied from the source materialsupply portion 1711 b is ozone. Note that the chemical formula oftetrakis(dimethylamide)hafnium is Hf[N(CH₃)₂]₄. Examples of anothermaterial include tetrakis(ethylmethylamide)hafnium. Note that nitrogenhas a function of eliminating charge trap states. Therefore, when theprecursor contains nitrogen, a hafnium oxide film having low density ofcharge trap states can be formed.

For example, in the case where an aluminum oxide layer is formed by adeposition apparatus utilizing an ALD method, two kinds of gases, e.g.,H₂O as an oxidizer and a precursor which is obtained by vaporizingliquid containing a solvent and an aluminum precursor compound (e.g.,trimethylaluminum (TMA)) are used. In this case, the first precursorsupplied from the source material supply portion 1711 a is TMA, and thesecond precursor supplied from the source material supply portion 1711 bis H₂O. Note that the chemical formula of trimethylaluminum is Al(CH₃)₃.Examples of another material liquid include tris(dimethylamide)aluminum,triisobutylaluminum, and aluminumtris(2,2,6,6-tetramethyl-3,5-heptanedionate).

<<Multi-Chamber Manufacturing Apparatus>>

FIG. 9B illustrates an example of a multi-chamber manufacturingapparatus including at least one deposition apparatus illustrated inFIG. 9A.

In the manufacturing apparatus illustrated in FIG. 9B, a stack of filmscan be successively formed without exposure to the air, and entry ofimpurities is prevented and throughput is improved.

The manufacturing apparatus illustrated in FIG. 9B includes at least aload chamber 1702, a transfer chamber 1720, a treatment chamber 1703, achamber 1701 which is a deposition chamber, and an unload chamber 1706.Note that in order to prevent attachment of moisture, the chambers ofthe manufacturing apparatus (including the load chamber, the treatmentchamber, the transfer chamber, the deposition chamber, the unloadchamber, and the like) are preferably filled with an inert gas (such asa nitrogen gas) whose dew point is controlled, more preferably maintainreduced pressure.

The chambers 1704 and 1705 may be deposition apparatuses utilizing anALD method like the chamber 1701, deposition apparatuses utilizing aplasma CVD method, deposition apparatuses utilizing a sputtering method,or deposition apparatuses utilizing a metal organic chemical vapordeposition (MOCVD) method.

For example, an example in which a stack of films is formed under acondition that the chamber 1704 is a deposition apparatus utilizing aplasma CVD method and the chamber 1705 is a deposition apparatusutilizing an MOCVD method is shown below.

Although FIG. 9B shows an example in which a top view of the transferchamber 1720 is a hexagon, a manufacturing apparatus in which the topsurface shape is set to a polygon having more than six corners and morechambers are connected depending on the number of layers of a stack maybe used. The top surface shape of the substrate is rectangular in FIG.9B; however, there is no particular limitation on the top surface shapeof the substrate. Although FIG. 9B shows an example of the single wafertype, a batch-type deposition apparatus in which films are deposited ona plurality of substrates at a time may be used.

<<Large Area ALD Apparatus>>

Moreover, with the plasma ALD method, a film can be deposited on a largesubstrate. FIGS. 10A and 10B are schematic views of other examples ofthe ALD apparatus. A gas which is made into plasma (precursor) isintroduced from an introduction port 810 into a chamber 820, and a filmcan be deposited on a substrate 800 from above and below through aplasma generation source 830 by an ALD method. The plasma generationsource 830 may be positioned in the chamber or outside the chamber. Asfor the deposition method, the film can be deposited with the substratefixed in the chamber as illustrated in FIG. 10A, or the film can bedeposited while the substrate is carried by an in-line method asillustrated in FIG. 10B. By using the plasma ALD method, the film can bedeposited with high throughput and in a large area.

In order to form a film uniformly on a side surface portion of thedisplay panel, film formation may be performed in the state where thedisplay panel is disposed on a susceptor or the like; alternatively, thesubstrate 100 of the display panel and a jig of a cassette may be inpoint contact, line contact, or surface contact.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 4

In this embodiment, the details of the display device described inEmbodiments 1 and 2 are described with reference to drawings.

FIGS. 11A and 11B are examples of a top view and a cross-sectional viewof the display device. Note that FIG. 11A illustrates a typicalstructure including the display panel 20, the display region 21, theperipheral circuit 22, and the FPC 42.

FIG. 11B is a cross-sectional view taken along the dashed lines A-A′,B-B′, C-C′, and D-D′ in FIG. 11A. The cross section taken along thedashed line A-A′ shows a peripheral portion of the display device, thecross section taken along the dashed line B-B′ shows the peripheralcircuit portion, the cross section taken along the dashed line C-C′shows the display region, and the cross section taken along the dashedline D-D′ shows a portion connected to an FPC.

<<Transistors 50 and 52>>

A transistor 50 can include a conductive layer 120, the insulating layer130, the insulating layer 131, a semiconductor layer 140, a conductivelayer 150, a conductive layer 160, and the insulating layer 170. Atransistor 52 can have the same structure. The transistor 50 can furtherinclude the insulating layer 181 or the insulating layer 182.

<<Dual-Gate Structure>>

A transistor 55, which is a modification example of the transistor 50,can be used as well. Description is given with reference to FIGS. 35A to35C. The transistor 55 illustrated in FIGS. 35A to 35C has a dual-gatestructure.

FIG. 35A is a top view of the transistor 55. FIG. 35B is across-sectional view taken along the dashed-dotted line X-X′ in FIG.35A, and FIG. 35C is a cross-sectional view taken along thedashed-dotted line Y-Y′ in FIG. 35A. Note that in FIG. 35A, thesubstrate 100, the insulating layer 110, the insulating layer 130, theinsulating layer 170, the insulating layer 180, and the like are notillustrated for the sake of clarity.

The transistor 55 illustrated in FIGS. 35A to 35C further includes aconductive layer 520 in addition to the layers included in thetransistor 50. The conductive layer 120 can be connected to theconductive layer 520 through an opening 530 formed in the insulatinglayers 130, 170, and 180.

<<Conductive Layer 520>>

The conductive layer 520 can be formed using a conductive film thattransmits visible light or a conductive film that reflects visiblelight. As the conductive film that transmits visible light, the samematerial as that of a conductive layer 190 to be described later can beused; for example, a material including one of indium (In), zinc (Zn),and tin (Sn) can be used. Typical examples of the conductive film thattransmits visible light include conductive oxides such as indium tinoxide, indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, indium zinc oxide, andindium tin oxide containing silicon oxide.

Alternatively, the conductive film that reflects visible light used forthe conductive layer 520 can be formed using the same material used fora conductive layer 220 to be described later.

Note that when a side surface of the semiconductor layer 140 faces theconductive layer 520 in the channel width direction as shown in FIG.35C, carriers flow not only at the interface between the insulatinglayer 170 and the semiconductor layer 140 and at the interface betweenthe insulating layer 130 and the semiconductor layer 140 but also in thesemiconductor layer 140. Therefore, the amount of transfer of carriersin the transistor 55 is increased. As a result, the on-state current andfield-effect mobility of the transistor 55 are increased. The electricfield of the conductive layer 520 affects the side surface or an endportion including the side surface and its vicinity of the semiconductorlayer 140; thus, generation of a parasitic channel at the side surfaceor the end portion of the semiconductor layer 140 can be suppressed.

By providing the transistor illustrated in FIGS. 35A to 35C in a pixelportion, signal delay in wirings can be reduced and display defects suchas display unevenness can be suppressed even though the number ofwirings is increased in a large-sized display device or ahigh-definition display device.

Note that all of transistors 52 included in the peripheral circuit (gatedriver and the like) may have the same structure or may have two or morekinds of structures. All of a plurality of transistors 50 included inthe pixel portion may have the same structure, or may have two or morekinds of structures.

Although an example of using a transistor including an oxidesemiconductor is shown in this embodiment, one embodiment of the presentinvention is not limited to this example. Depending on the case orcircumstances, a transistor including a semiconductor material that isnot an oxide semiconductor may be used in one embodiment of the presentinvention.

<<Reflective Liquid Crystal Panel>>

As the display panel mounted in the display device, a reflective liquidcrystal panel can be used as illustrated in FIG. 11B. In the displaydevice 10 illustrated in FIG. 11B, the liquid crystal element 80 is usedas a display element. The display device 10 includes a polarizing plate103, a polarizing plate 303, a protection substrate 105, a protectionsubstrate 302, a bonding layer 373, a bonding layer 374, a bonding layer375, and a bonding layer 376. In the case of a reflective liquid crystalpanel, part or whole of the pixel electrode functions as a reflectiveelectrode (described later). In that case, a memory circuit such as anSRAM can be provided under the reflective electrode, which can furtherreduce the power consumption.

Other examples of the liquid crystal panel include a transmissive liquidcrystal panel (described later), a semi-transmissive liquid crystalpanel, a direct-view liquid crystal panel, and a projection liquidcrystal panel.

<<Substrate 100>>

There is no particular limitation on a material and the like of asubstrate 100 as long as the material has heat resistance high enough towithstand at least heat treatment performed later. The substrate 100desirably has a high light-transmitting property.

For the substrate 100, an organic material, an inorganic material, acomposite material of an organic material and an inorganic material, orthe like can be used. For example, an inorganic material such as glass,a ceramic, or a metal can be used for the substrate 100.

Specifically, non-alkali glass, soda-lime glass, potash glass, crystalglass, or the like can be used for the substrate 100. An inorganic oxidefilm, an inorganic nitride film, an inorganic oxynitride film, or thelike can be used for the substrate 100. For example, silicon oxide,silicon nitride, silicon oxynitride, alumina, or the like can be usedfor the substrate 100. Stainless steel, aluminum, or the like can beused for the substrate 100.

A single-layer material or a stacked-layer material in which a pluralityof layers are stacked can be used for the substrate 100. For example, astacked-layer material in which a base, an insulating film that preventsdiffusion of impurities contained in the base, and the like are stackedcan be used for the substrate 100. Specifically, a stacked-layermaterial in which glass and one or a plurality of films that preventdiffusion of impurities contained in the glass and that are selectedfrom a silicon oxide layer, a silicon nitride layer, a siliconoxynitride layer, and the like are stacked can be used for the substrate100. Alternatively, a stacked-layer material in which a resin and a filmfor preventing diffusion of impurities that penetrate the resin, such asa silicon oxide film, a silicon nitride film, and a silicon oxynitridefilm are stacked can be used for the substrate 100.

The above-described substrate that can be used as the substrate 100 canbe used as the substrate 300 as well.

<<Insulating Layer 110>>

The insulating layer 110 that functions as a base film is formed usingsilicon oxide, silicon oxynitride, silicon nitride, silicon nitrideoxide, gallium oxide, hafnium oxide, yttrium oxide, aluminum oxide,aluminum oxynitride, or the like. Note that when silicon nitride,gallium oxide, hafnium oxide, yttrium oxide, aluminum oxide, or the likeis used as a material for the insulating layer 110, it is possible tosuppress diffusion of impurities such as alkali metal, water, andhydrogen into the semiconductor layer 140 from the substrate 100. Theinsulating layer 110 is formed over the substrate 100. The insulatinglayer 110 is not necessarily provided.

<<Conductive Layer 120>>

The conductive layer 120 that functions as a gate electrode is formedusing a metal element selected from aluminum, chromium, copper,tantalum, titanium, molybdenum, nickel, iron, cobalt, and tungsten; analloy containing any of these metal elements as a component; an alloycontaining any of these metal elements in combination; or the like.Furthermore, one or more metal elements selected from manganese andzirconium may be used. The conductive layer 120 may have a single-layerstructure or a layered structure of two or more layers. For example, anyof the following can be used: a single-layer structure of an aluminumfilm containing silicon; a single-layer structure of a copper filmcontaining manganese; a two-layer structure in which a titanium film isstacked over an aluminum film; a two-layer structure in which a titaniumfilm is stacked over a titanium nitride film; a two-layer structure inwhich a tungsten film is stacked over a titanium nitride film; atwo-layer structure in which a tungsten film is stacked over a tantalumnitride film or a tungsten nitride film; a two-layer structure in whicha copper film is stacked over a copper film containing manganese; athree-layer structure in which a titanium film, an aluminum film, and atitanium film are stacked in this order; a three-layer structure inwhich a copper film containing manganese, a copper film, and a copperfilm containing manganese are stacked in this order; and the like.Alternatively, an alloy film or a nitride film which contains aluminumand one or more elements selected from titanium, tantalum; tungsten,molybdenum, chromium, neodymium, and scandium may be used.

<<Insulating Layer 130>>

The insulating layer 130 functions as a gate insulating film. Theinsulating layer 130 can be formed using, for example, an insulatingfilm containing at least one of aluminum oxide, magnesium oxide, siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride,gallium oxide, germanium oxide, yttrium oxide, zirconium oxide,lanthanum oxide, neodymium oxide, hafnium oxide, and tantalum oxide. Theinsulating layer 130 may contain lanthanum (La), nitrogen, or zirconium(Zr) as an impurity. For the insulating layer 130, for example, siliconoxynitride can be used.

<<Insulating Layer 131>>

The stacked insulating layers 130 and 131 can be used as the gateinsulating film. For the insulating layer 131, the same material usedfor the insulating layer 130 can be used. For example, silicon nitridecan be used for the insulating layer 131. Use of the insulating layer131 can prevent entry of hydrogen, water, and the like from the outsideto the semiconductor layer 140.

<<Semiconductor Layer 140>>

The semiconductor layer 140 is formed with a metal oxide containing atleast In or Zn. The area of a top surface of the semiconductor layer 140is preferably equal to or smaller than the area of a top surface of theconductive layer 120.

<<Oxide Semiconductor>>

As an oxide semiconductor used for the aforementioned semiconductorlayer 140, any of the following can be used, for example: anIn—Ga—Zn-based oxide, an In—Al—Zn-based oxide, an In—Sn—Zn-based oxide,an In—Hf—Zn-based oxide, an In—La—Zn-based oxide, an In—Ce—Zn-basedoxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide, anIn—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-based oxide,an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, an In—Ho—Zn-basedoxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide, anIn—Yb—Zn-based oxide, an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-basedoxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, anIn—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, anIn—Hf—Al—Zn-based oxide, and an In—Ga-based oxide.

Note that here, an “In—Ga—Zn-based oxide” means an oxide containing In,Ga, and Zn as its main components and there is no limitation on theratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain another metalelement in addition to In, Ga, and Zn.

When the semiconductor layer 140 is formed using an In-M-Zn oxide, theatomic ratio of In to M when the summation of In and M is assumed to be100 atomic % is preferably as follows: the proportion of In is higherthan 25 atomic % and the proportion of M is lower than 75 atomic %;further preferably, the proportion of In is higher than 34 atomic % andthe proportion of M is lower than 66 atomic %.

The energy gap of the semiconductor layer 140 is 2 eV or more,preferably 2.5 eV or more, and further preferably 3 eV or more. With theuse of an oxide semiconductor having such a wide energy gap, theoff-state current of the transistor 50 can be reduced.

The thickness of the semiconductor layer 140 desirably ranges from 3 nmto 200 nm, preferably from 3 nm to 100 mu, and further preferably from 3nm to 50 nm. In the case where the oxide semiconductor layer 140 isformed using an In-M-Zn oxide (M is Al, Ga, Y, Zr, La, Ce, or Nd, and isnot limited to a natural number), it is preferable that the atomic ratioof metal elements of a sputtering target used for forming the In-M-Znoxide be In:M:Zn=1:1:1, In: M Zn=1:1:1.2, In: M Zn 1:1:1.5,In:M:Zn=2:1:3, In:M:Zn=3:1:2, In:M:Zn=4:2:4.1. Note that the atomicratio of metal elements in the formed semiconductor layer 140 variesfrom the above atomic ratio of metal elements of the sputtering targetwithin a range of ±40% as an error. Note that a c-axis alignedcrystalline oxide semiconductor (CAAC-OS) film and a microcrystallineoxide semiconductor film that are described later can be formed using atarget including an In—Ga—Zn oxide, preferably a polycrystalline targetincluding an In—Ga—Zn oxide.

Hydrogen contained in the semiconductor layer 140 reacts with oxygenbonded to a metal atom to be water, and also causes oxygen vacancies ina lattice from which oxygen is released (or a portion from which oxygenis released). Due to entry of hydrogen into the oxygen vacancies, anelectron serving as a carrier is generated. Further, in some cases,bonding of part of hydrogen to oxygen bonded to a metal atom causesgeneration of an electron serving as a carrier. Thus, a transistorincluding an oxide semiconductor which contains hydrogen is likely to benormally on.

Accordingly, it is preferable that hydrogen as well as the oxygenvacancies in the semiconductor layer 140 be reduced as much as possible.Specifically, in the semiconductor layer 140, the concentration ofhydrogen which is measured by secondary ion mass spectrometry (SIMS) isset to lower than or equal to 5×10¹⁹ atoms/cm³, preferably lower than orequal to 1×10¹⁹ atoms/cm³, further preferably lower than or equal to5×10¹⁸ atoms/cm³, still further preferably lower than or equal to 1×10¹⁸atoms/cm³, yet still further preferably lower than or equal to 5×10¹⁷atoms/cm³, and still more preferably lower than or equal to 1×10¹⁶atoms/cm³. As a result, the transistor 50 has a positive thresholdvoltage (also referred to as nominally-off characteristics).

When silicon or carbon which is one of the elements belonging to Group14 is contained in the semiconductor layer 140, oxygen vacancies areincreased in the semiconductor layer 140, and the semiconductor layer140 has n-type conductivity. Thus, the concentration of silicon orcarbon (the concentration is measured by SIMS) in the semiconductorlayer 140 is lower than or equal to 2×10¹⁸ atoms/cm³, preferably lowerthan or equal to 2×10¹⁷ atoms/cm³. As a result, the transistor 50 has apositive threshold voltage (also referred to as normally-offcharacteristics).

Furthermore, the concentration of alkali metal or alkaline earth metalin the semiconductor layer 140, which is measured by SIMS, is lower thanor equal to 1×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁶atoms/cm³. Alkali metal and alkaline earth metal might generate carrierswhen bonded to an oxide semiconductor, in which case the off-statecurrent of the transistor might be increased. Therefore, it ispreferable to reduce the concentration of alkali metal or alkaline earthmetal in the semiconductor layer 140. As a result, the transistor 50 hasa positive threshold voltage (also referred to as normally-offcharacteristics).

Furthermore, when nitrogen is contained in the semiconductor layer 140,electrons serving as carriers are generated to increase the carrierdensity, so that the semiconductor layer 140 easily has n-typeconductivity. Thus, the transistor tends to have normally-oncharacteristics. For this reason, nitrogen in the semiconductor layer140 is preferably reduced as much as possible; for example, theconcentration of nitrogen which is measured by SIMS is preferably set tolower than or equal to 5×10¹⁸ atoms/cm³.

When impurities in the semiconductor layer 140 are reduced, the carrierdensity of the semiconductor layer 140 can be lowered. The carrierdensity of the semiconductor layer 140 is 1×10¹⁵/cm³ or less, preferably1×10¹³/cm³ or less, further preferably 8×10¹¹/cm³ or less, furtherpreferably less than 1×10¹¹/cm³, further preferably less than1×10¹⁰/cm³, and 1×10⁻⁹/cm³ or more.

When an oxide semiconductor having a low impurity concentration and alow density of defect states is used for the semiconductor layer 140,the transistor can have more excellent electrical characteristics. Here,the state in which impurity concentration is low and the density ofdefect states is low (the amount of oxygen vacancies is small) isreferred to as “highly purified intrinsic” or “substantially highlypurified intrinsic.” A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor has few carrier generationsources, and thus has a low carrier density in some cases. Thus, thetransistor whose channel region is formed in the semiconductor layer 140including the oxide semiconductor is likely to have a positive thresholdvoltage (also referred to as normally-off characteristics). A highlypurified intrinsic or substantially highly purified intrinsic oxidesemiconductor has a low density of defect states and accordingly has alow density of trap states in some cases. The transistor including thesemiconductor layer 140 containing the highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor has anextremely low off-state current; the off-state current can be less thanor equal to the measurement limit of a semiconductor parameter analyzer,i.e., less than or equal to 1×10⁻¹³ A, at a voltage (drain voltage)between a source electrode and a drain electrode of from 1 V to 10 V. Inaddition, variation in characteristics can be prevented.

In the case where the voltage between a source and a drain is set toabout 0.1 V, 5 V, or 10 V, for example, the off-state currentstandardized on the channel width of the transistor 50 in which thesemiconductor layer 140 is used for the semiconductor layer can be aslow as several yoctoamperes per micrometer to several zeptoamperes permicrometer.

When a transistor with an extremely low off-state leakage current isused as the transistor 50 connected to a display element (e.g., theliquid crystal element 80), the time for holding image signals can beextended. For example, images can be held even when the frequency ofwriting image signals is more than or equal to 11.6 (once a day) andless than 0.1 Hz (0.1 times a second), preferably more than or equal to0.28 mHz (once an hour) and less than 1 Hz (once a second). Thus, thefrequency of writing image signals can be reduced, which leads to areduction in power consumption of the display panel 20. Needless to say,the frequency of writing image signals can be more than or equal to 1Hz, preferably more than or equal to 30 Hz (30 times a second), furtherpreferably more than or equal to 60 Hz (60 times a second) and less than960 Hz (960 times a second).

From the above reason, the use of a transistor containing an oxidesemiconductor allows fabrication of a highly reliable display panel withlow power consumption.

In the transistor including an oxide semiconductor, the semiconductorlayer 140 can be formed by a sputtering method, a metal organic chemicalvapor deposition (MOCVD) method, or a pulse laser deposition (PLD)method, for example. In the case where the semiconductor layer 140 isformed by a sputtering method, a large-area display device can bemanufactured.

Note that instead of the semiconductor layer 140, a semiconductor layerincluding silicon or silicon germanium may be used. The semiconductorlayer including silicon or silicon germanium can have an amorphousstructure, a polycrystalline structure, or a single crystal structure,as appropriate.

<<Conductive Layers 150 and 160>>

Each of the conductive layers 150 and 160 has a function of a sourceelectrode, a drain electrode, or an electrode of a capacitor. Theconductive layers 150 and 160 are formed using a metal element selectedfrom aluminum, chromium, copper, tantalum, titanium, molybdenum, nickel,iron, cobalt, and tungsten; an alloy containing any of these metalelements as a component; an alloy containing any of these metal elementsin combination; or the like. Furthermore, one or more metal elementsselected from manganese and zirconium may be used. The conductive layers150 and 160 may have a single-layer structure or a layered structure oftwo or more layers. For example, any of the following can be used: asingle-layer structure of an aluminum film containing silicon; asingle-layer structure of a copper film containing manganese; atwo-layer structure in which a titanium film is stacked over an aluminumfilm; a two-layer structure in which a titanium film is stacked over atitanium nitride film; a two-layer structure in which a tungsten film isstacked over a titanium nitride film; a two-layer structure in which atungsten film is stacked over a tantalum nitride film or a tungstennitride film; a two-layer structure in which a copper film is stackedover a copper film containing manganese; a three-layer structure inwhich a titanium film, an aluminum film, and a titanium film are stackedin this order; a three-layer structure in which a copper film containingmanganese, a copper film, and a copper film containing manganese arestacked in this order; and the like. Alternatively, an alloy film or anitride film which contains aluminum and one or more elements selectedfrom titanium, tantalum, tungsten, molybdenum, chromium, neodymium, andscandium may be used.

<<Insulating Layer 170>>

The insulating layer 170 has a function of protecting the channel regionof the transistor. The insulating layer 170 is formed using an oxideinsulating film such as silicon oxide, silicon oxynitride, aluminumoxide, aluminum oxynitride, gallium oxide, gallium oxynitride, yttriumoxide, yttrium oxynitride, hafnium oxide, or hafnium oxynitride, or anitride insulating film such as silicon nitride or aluminum nitride. Theinsulating layer 170 can have a single-layer structure or astacked-layer structure.

The insulating layer 170 is preferably formed using an oxide insulatingfilm containing more oxygen than that in the stoichiometric composition.Part of oxygen is released by heating from the oxide insulating filmcontaining more oxygen than that in the stoichiometric composition. Theoxide insulating film containing more oxygen than that in thestoichiometric composition is an oxide insulating film of which theamount of released oxygen atoms is greater than or equal to 1.0×10¹⁸atoms/cm³, preferably greater than or equal to 3.0×10²⁰ atoms/cm³ inthemial desorption spectroscopy (TDS) analysis in which heat treatmentis performed such that a temperature of a film surface is higher than orequal to 100° C. and lower than or equal to 700° C. or higher than orequal to 100° C. and lower than or equal to 500° C. By the heattreatment, oxygen contained in the insulating layer 170 can betransferred to the semiconductor layer 140, so that the amount of oxygenvacancies in the semiconductor layer 140 can be reduced.

<<Insulating Layer 180>>

When an insulating film having a blocking effect against oxygen,hydrogen, water, and the like is provided as the insulating layer 180,it is possible to prevent outward diffusion of oxygen from thesemiconductor layer 140 and entry of hydrogen, water, or the like intothe semiconductor layer 140 from the outside. The insulating layer 180can be formed using, for example, an insulating film containing at leastone of aluminum oxide, magnesium oxide, silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, gallium oxide,germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide,neodymium oxide, hafnium oxide, and tantalum oxide. The insulating layer180 may be a stack of any of the above materials. The insulating layer180 may contain lanthanum (La), nitrogen, or zirconium (Zr) as animpurity.

<<Insulating Layer 181>>

The insulating layer 181 has a function of making a flat surface. Aninorganic material or an organic material can be used for the insulatinglayer 181. For example, an oxide insulating film of silicon oxide,silicon oxynitride, aluminum oxide, aluminum oxynitride, gallium oxide,gallium oxynitride, yttrium oxide, yttrium oxynitride, hafnium oxide,hafnium oxynitride, or the like; a nitride insulating film of siliconnitride, aluminum nitride, or the like; or a heat-resistant organicmaterial such as a polyimide resin, an acrylic resin, a polyimide amideresin, a benzocyclobutene resin, a polyamide resin, or an epoxy resincan be used.

<<Insulating Layer 182>>

When an insulating film having a blocking effect against oxygen,hydrogen, water, and the like is provided as the insulating layer 182,the insulating layer 182 in addition to the insulating layer 180 canprevent outward diffusion of oxygen from the semiconductor layer 140 andentry of hydrogen, water, or the like into the semiconductor layer 140from the outside. The insulating layer 182 can be formed using, forexample, an insulating film containing at least one of aluminum oxide,magnesium oxide, silicon oxide, silicon oxynitride, silicon nitrideoxide, silicon nitride, gallium oxide, germanium oxide, yttrium oxide,zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide, andtantalum oxide. The insulating layer 182 may be a stack of any of theabove materials. The insulating layer 182 may contain lanthanum (La),nitrogen, or zirconium (Zr) as an impurity.

<<Liquid Crystal Element 80>>

The liquid crystal element 80 can be driven in a twisted nematic (TN)mode, for example. The liquid crystal element 80 includes a liquidcrystal layer 390, the conductive layer 220, and the conductive layer380.

Although not illustrated in FIGS. 11A and 11B, an alignment film may beprovided on a side of the conductive layer 220 in contact with theliquid crystal layer 390 and on a side of the conductive layer 380 incontact with the liquid crystal layer 390.

Since the liquid crystal layer 390 is sandwiched between the conductivelayer 220 and the conductive layer 380, liquid crystal molecules can becontrolled by an electric field generated therebetween. As a method fordriving a display device using a liquid crystal element, for example, anSTN mode, a VA mode, an axially symmetric aligned micro-cell (ASM) mode,an optically compensated birefringence (OCB) mode, a ferroelectricliquid crystal (FLC) mode, an antiferroelectric liquid crystal (AFLC)mode, an MVA mode, a patterned vertical alignment (PVA) mode, anin-plane switching (IPS) mode, or a transverse bend alignment (TBA) modemay be used. Other examples of the driving method of the display deviceinclude an electrically controlled birefringence (ECB) mode, a polymerdispersed liquid crystal (PDLC) mode, a polymer network liquid crystal(PNLC) mode, and a guest-host mode. Note that one embodiment of thepresent invention is not limited to the above, and various liquidcrystal elements and driving methods can be employed.

The liquid crystal element 80 may be formed using a liquid crystalcomposition including a liquid crystal exhibiting a nematic phase and achiral material. In that case, a cholesteric phase or a blue phase isexhibited. The liquid crystal exhibiting a blue phase has a shortresponse time of 1 msec or less. Since the liquid crystal exhibiting ablue phase is optically isotropic, alignment treatment is not necessaryand viewing angle dependence is small.

<<Conductive Layer 220>>

For the conductive layer 220 that reflects visible light, for example, ametal material such as aluminum, gold, platinum, silver, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or analloy containing any of these metal materials can be used. Lanthanum,neodymium, germanium, or the like may be added to the metal material orthe alloy. Furthermore, an alloy containing aluminum (an aluminum alloy)such as an alloy of aluminum and titanium, an alloy of aluminum andnickel, an alloy of aluminum and neodymium, or an alloy of aluminum,nickel, and lanthanum (Al—Ni—La), or an alloy containing silver such asan alloy of silver and copper, an alloy of silver, palladium, and copper(Ag—Pd—Cu, also referred to as APC), or an alloy of silver and magnesiumcan be used for the conductive film. An alloy of silver and copper ispreferable because of its high heat resistance. A metal film or a metaloxide film is stacked on an aluminum alloy film, whereby oxidation ofthe aluminum alloy film can be suppressed. Examples of a material forthe metal film or the metal oxide film are titanium and titanium oxide.Alternatively, the conductive film having a property of transmittingvisible light and a film containing any of the above metal materials maybe stacked. For example, a stacked film of silver and ITO or a stackedfilm of an alloy of silver and magnesium and ITO can be used.

<<Capacitors 60 and 62>>

A capacitor 60 can include the conductive layer 120, the insulatinglayer 130, the insulating layer 131, and the conductive layer 160. Theconductive layer 120 has a function of one electrode of a capacitor 60.The conductive layer 160 has a function of the other electrode of thecapacitor 60. The insulating layer 130 and the insulating layer 131 arepositioned between the conductive layer 120 and the conductive layer160. The capacitor 62 can have the same structure as the capacitor 60.

<<Conductive Layer 380>>

The conductive layer 380 is formed using a conductive film thattransmits visible light. For example, a material including one of indium(In), zinc (Zn), and tin (Sn) can be used for the conductive film thattransmits visible light. Typical examples of the conductive film thattransmits visible light include conductive oxides such as indium tinoxide, indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, indium zinc oxide, andindium tin oxide containing silicon oxide.

<<Insulating Layer 330>>

The insulating layer 330 has a function of making a flat surface. Aninorganic material or an organic material can be used for the insulatinglayer 330. For example, an oxide insulating film of silicon oxide,silicon oxynitride, aluminum oxide, aluminum oxynitride, gallium oxide,gallium oxynitride, yttrium oxide, yttrium oxynitride, hafnium oxide,hafnium oxynitride, or the like; a nitride insulating film of siliconnitride, aluminum nitride, or the like; or a heat-resistant organicmaterial such as a polyimide resin, an acrylic resin, a polyimide amideresin, a benzocyclobutene resin, a polyamide resin, or an epoxy resincan be used.

<<Coloring Layer 360>>

A coloring layer 360 transmits light in a specific wavelength range. Forexample, a color filter that transmits light in a specific wavelengthrange, such as red, green, blue, or yellow light, can be used. Eachcoloring layer is formed in a desired position with any of variousmaterials by a printing method, an inkjet method, an etching methodusing a photolithography method, or the like. In a white pixel, a resinsuch as a transparent resin or a white resin may overlap with thelight-emitting element.

<<Light-Blocking Layer 18>>

A light-blocking material can be used for the light-blocking layer 18. Aresin in which a pigment is dispersed, a resin containing a dye, or aninorganic film such as a black chromium film can be used for thelight-blocking layer 18. Carbon black, an inorganic oxide, a compositeoxide containing a solid solution of a plurality of inorganic oxides, orthe like can be used for the light-blocking layer 18.

<<Spacer 240>>

An insulating material can be used for a spacer 240. For example, aninorganic material, an organic material, or a stacked-layer material ofan inorganic material and an organic material can be used. Specifically,a film containing silicon oxide, silicon nitride, or the like, acrylic,polyimide, a photosensitive resin, or the like can be used.

<<Adhesive layer 370>>

An inorganic material, an organic material, a composite material of aninorganic material and an organic material, or the like can be used forthe adhesive layer 370.

For example, an organic material such as a light curable adhesive, areactive curable adhesive, a thermosetting adhesive, and/or an anaerobicadhesive can be used for the adhesive layer 370. Note that each of theadhesives can be used alone or in combination.

The light curable adhesive refers to, for example, an adhesive that iscured by ultraviolet rays, an electron beam, visible light, infraredlight, or the like.

Specifically, an adhesive containing an epoxy resin, an acrylic resin, asilicone resin, a phenol resin, a polyimide resin, an imide resin, apolyvinyl chloride (PVC) resin, a polyvinyl butyral (PVB) resin, anethylene vinyl acetate (EVA) resin, silica, or the like can be used forthe adhesive layer 370.

The material is cured rapidly particularly when a light curable adhesiveis used, leading to shortening of the process time. In addition,influence of the film formation step can be inhibited because curingstarts with light irradiation. In addition, involuntary curing of theadhesive due to environment can be prevented because curing starts withlight irradiation. Furthermore, curing can be performed at lowtemperatures to facilitate the control of process environment. From theabove reasons, the use of a light curable adhesive shortens the processtime and reduces processing costs.

<<FPC 42>>

The FPC 42 is electrically connected to the conductive layer 160 throughan anisotropic conductive film 510. An image signal and the like can besupplied from the FPC 42 to the driver circuit including the transistor52, the capacitor 62, and the like.

<Insulating Layers 181 and 182 with Unevenness>

The insulating layer 181 and the insulating layer 182 can haveunevenness in a pixel region, and thus external light that enters theconductive layer 220 and reflects can be scattered. Accordingly, lightreflection can be prevented.

<Insulating Layers 181 and 182 without Unevenness and Scattering Film304>

Alternatively, the insulating layer 181 and the insulating layer 182 donot necessarily have unevenness. FIG. 12 is a cross-sectional view ofanother structure of the display device illustrated in FIGS. 11A and11B. In this case, a scattering film 304 and a bonding layer 377 areprovided on the viewer side of the substrate 300 (the top surface sideof the display device), whereby the same effect as that in FIGS. 11A and11B can be obtained.

<Shape 1 of Substrate Edge of Display Device>

FIG. 13 is a cross-sectional view of another structure of the displaydevice illustrated in FIG. 11B. The protection film 23 in FIG. 13 inwhich an edge of the substrate does not have unevenness as in FIG. 1Ccan be formed by an ALD method.

<Shape 2 of Substrate Edge of Display Device>

The protection film 23 can be formed in a selected region on a surfaceand a side surface of the display device 10. FIG. 14 and FIG. 15 arecross-sectional views of the display devices.

FIG. 14 shows a structure in which the protection film 23 is hardlydeposited on the rear surface of the display device (on the substrate100 side) as illustrated in FIG. 2A. For example, in the structure ofFIG. 14, with use of a mask, the protection film 23 can be preventedfrom being deposited on the rear surface and an upper surface of the FPC42. In that case, the protection film may cover an edge of the substrate100 or the substrate 300 as illustrated in a region 13. Alternatively,as illustrated in FIG. 15, the region 14 in which the protection film isnot deposited on the rear surface can be provided by the methodillustrated in FIGS. 7A to 7D.

<Shape 3 of Substrate Edge of Display Device>

FIG. 16, FIG. 17, and FIG. 18 show structural examples of the displaydevice 10 which are different from the above-described structuralexamples. The structure of FIG. 16 employs the structure of FIG. 4A. Thestructure of FIG. 17 employs the structure of FIG. 4B. The structure ofFIG. 18 employs the structure of FIG. 5A. In each of the structures, byproviding the protection film 23, entry of atmospheric components suchas water can be prevented and the insulating layer 182 can be omitted.

In the structure of FIG. 18, the protection film 23 can be formed moreuniformly by making the area of the substrate 300 smaller than the areaof the substrate 100.

<Shape 4 of Substrate Edge of Display Device>

FIG. 19 shows another structural example of the display device 10. Thestructure of FIG. 19 employs the structure of FIG. 6A, and can omit theinsulating layer 181 and the insulating layer 182 by including theprotection film 23.

<Combination of Display Device and Touch Sensor>

The display device 10 can be combined with a touch sensor to form atouch panel. FIG. 20 and FIG. 21 are cross-sectional views of touchpanels. A structure illustrated in FIG. 20 in which a conductive layer410 and a conductive layer 430 are used for an electrode (wiring) of atouch sensor can be employed. The conductive layer 380 used in a displaypanel can be used for the wiring of the touch sensor. By using theconductive layer 380 in combination with the conductive layer 410, theconductive layer 430, the insulating layer 420, and the insulating layer440, an in-cell touch panel can be formed. Note that the electrode ofthe touch sensor may be formed on the viewer side (the top surface side)or the inner side (the display element side) of the substrate 300.

<<Conductive Layers 410 and 430>>

The conductive layer 410 is formed using a metal element selected fromaluminum, chromium, copper, tantalum, titanium, molybdenum, nickel,iron, cobalt, and tungsten; an alloy containing any of these metalelements as a component; an alloy containing any of these metal elementsin combination; or the like. Further, one or more metal elementsselected from manganese and zirconium may be used.

The conductive layer 410 may have a single-layer structure or a layeredstructure of two or more layers. For example, any of the following canbe used: a single-layer structure of an aluminum film containingsilicon; a single-layer structure of a copper film containing manganese;a two-layer structure in which a titanium film is stacked over analuminum film; a two-layer structure in which a titanium film is stackedover a titanium nitride film; a two-layer structure in which a tungstenfilm is stacked over a titanium nitride film; a two-layer structure inwhich a tungsten film is stacked over a tantalum nitride film or atungsten nitride film; a two-layer structure in which a copper film isstacked over a copper film containing manganese; a three-layer structurein which a titanium film, an aluminum film, and a titanium film arestacked in this order; a three-layer structure in which a copper filmcontaining manganese, a copper film, and a copper film containingmanganese are stacked in this order; and the like. Alternatively, analloy film or a nitride film which contains aluminum and one or moreelements selected from titanium, tantalum, tungsten, molybdenum,chromium, neodymium, and scandium may be used.

Alternatively, as a material of the conductive films such as theconductive layer 410, that is, wirings and electrodes forming the touchpanel, a transparent conductive film containing indium oxide, tin oxide,zinc oxide, or the like (e.g., ITO) can be given. Moreover, for example,a low-resistance material is preferably used as the material of thewiring and the electrode in the touch panel. For example, silver,copper, aluminum, a carbon nanotube, graphene, or a metal halide (suchas a silver halide) may be used. Alternatively, a metal nanowireincluding a plurality of conductors with an extremely small width (e.g.,a diameter of several nanometers) may be used. Further alternatively, anet-like metal mesh with a conductor may be used. Examples of suchmaterials include an Ag nanowire, a Cu nanowire, an Al nanowire, an Agmesh, a Cu mesh, and an Al mesh. For example, in the case of using an Agnanowire for the wiring and the electrode in the touch panel, a visiblelight transmittance of 89% or more and a sheet resistance of 40 Ω/sq. ormore and 100 Ω/sq. or less can be achieved.

A metal nanowire, a metal mesh, a carbon nanotube, graphene, and thelike, which are examples of a material that can be used for theabove-described wiring and electrode in the touch panel, have a highvisible light transmittance; therefore, they may be used for anelectrode of a display element (e.g., a pixel electrode or a commonelectrode). The conductive layer 430 can be formed using a film similarto that used to form the conductive layer 410.

<<Insulating Layer 420 and Insulating Layer 440>>

An inorganic material or an organic material can be used for theinsulating layer 420. For example, an oxide insulating film of siliconoxide, silicon oxynitride, aluminum oxide, aluminum oxynitride, galliumoxide, gallium oxynitride, yttrium oxide, yttrium oxynitride, hafniumoxide, hafnium oxynitride, or the like; a nitride insulating film ofsilicon nitride, aluminum nitride, or the like; or a heat-resistantorganic material such as a polyimide resin, an acrylic resin, apolyimide amide resin, a benzocyclobutene resin, a polyamide resin, oran epoxy resin can be used. The insulating layer 440 can be formed withthe same film as the insulating layer 420.

<<Transmissive Liquid Crystal Panel>>

As the display panel mounted in the display device, a transmissiveliquid crystal panel can be used as illustrated in FIG. 22. In thedisplay device illustrated in FIG. 22, the liquid crystal element 81 isused as a display element. The display device includes the polarizingplate 103, the polarizing plate 303, a backlight 104, and bonding layers373, 374, and 375. The protection substrate 302 is provided on the outerside (the viewer side) than the polarizing plate 303 and bonded with thebonding layer 376. Note that the same components (e.g., transistors)used in the reflective liquid crystal panel can be formed in the samemanner as the reflective liquid crystal panel.

<<Liquid Crystal Element 81>>

The liquid crystal element 81 can be driven in a fringe field switching(FFS) mode. The liquid crystal element 81 includes the liquid crystallayer 390 and the conductive layer 190. Since the liquid crystal layer390 receives an electric field from the conductive layer 190 in thehorizontal direction, liquid crystal molecules included in the liquidcrystal layer 390 can be controlled.

<<Conductive Layer 190>>

The conductive layer 190 is formed using a conductive film thattransmits visible light. For example, a material including one of indium(In), zinc (Zn), and tin (Sn) can be used for the conductive film thattransmits visible light. Typical examples of the conductive film thattransmits visible light include conductive oxides such as indium tinoxide, indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, indium zinc oxide, andindium tin oxide containing silicon or silicon oxide.

<<Capacitor 61, 63>>

A capacitor 61 includes the conductive layer 400, the insulating layer180, and the conductive layer 190. The conductive layer 400 functions asone electrode of the capacitor 61. The conductive layer 190 functions asthe other electrode of the capacitor 61. The insulating layer 130 isprovided between the conductive layer 400 and the conductive layer 190.A capacitor 63 can have a structure similar to that of the capacitor 61.

<<Conductive Layer 400>>

When the transistor 50 includes an oxide semiconductor in thesemiconductor layer 140, the conductive layer 400 can be formed with thesame material as the semiconductor layer 140. In that case, theconductive layer 400 is formed by processing a film formed at the sametime as the semiconductor layer 140. The conductive layer 400 has acrystal structure similar to or different from that of the semiconductorlayer 140. When the film formed at the same time as the semiconductorlayer 140 includes impurities or oxygen vacancies, the film can haveconductivity; thus, the conductive layer 400 is formed. Typical examplesof the impurities included in the conductive layer 400 are a rare gas,hydrogen, boron, nitrogen, fluorine, aluminum, and phosphorus. Typicalexamples of the rare gas are helium, neon, argon, krypton, and xenon.Although an example where the conductive layer 400 has conductivity isshown, one embodiment of the present invention is not limited to thisexample. Depending on circumstances or conditions, the conductive layer400 does not necessarily have conductivity. In other words, theconductive layer 400 may have properties similar to those of thesemiconductor layer 140.

Although the semiconductor layer 140 and the conductive layer 400 areformed over the insulating layer 130 as described above, they havedifferent impurity concentrations. Specifically, the impurityconcentration of the conductive layer 400 is higher than that of thesemiconductor layer 140. For example, in the semiconductor layer 140,the hydrogen concentration measured by secondary ion mass spectrometryis lower than or equal to 5×10¹⁹ atoms/cm³, preferably lower than orequal to 5×10¹⁸ atoms/cm³, further preferably lower than or equal to1×10¹⁸ atoms/cm³, still further preferably lower than or equal to 5×10¹⁷atoms/cm³, and yet still further preferably lower than or equal to1×10¹⁶ atoms/cm³. In contrast, the hydrogen concentration in theconductive layer 400 measured by secondary ion mass spectrometry ishigher than or equal to 8×10¹⁹ atoms/cm³, preferably higher than orequal to 1×10²⁰ atoms/cm³, and further preferably higher than or equalto 5×10²⁰ atoms/cm³. In addition, the hydrogen concentration in theconductive layer 400 is greater than or equal to 2 times or greater thanor equal to 10 times that in the semiconductor layer 140.

When an oxide semiconductor film formed at the same time as thesemiconductor layer 140 is exposed to plasma, the oxide semiconductorfilm is damaged and oxygen vacancies can be generated. For example, whena film is formed over the oxide semiconductor film by a plasma CVDmethod or a sputtering method, the oxide semiconductor film is exposedto plasma and oxygen vacancies are generated. Alternatively, when theoxide semiconductor film is exposed to plasma in etching treatment forformation of an opening in the insulating layer 170, oxygen vacanciesare generated. Alternatively, when the oxide semiconductor film isexposed to plasma of a mixed gas of oxygen and hydrogen, hydrogen, arare gas, ammonia, and the like, oxygen vacancies are generated.Alternatively, when impurities are added to the oxide semiconductorfilm, oxygen vacancies can be formed while the impurities are added tothe oxide semiconductor film. The impurities can be added by an iondoping method, an ion implantation method, a plasma treatment method,and the like. In the plasma treatment method, plasma is generated in agas atmosphere containing the impurities to be added, and ions of theimpurities accelerated by plasma treatment are made to collide with theoxide semiconductor film, whereby oxygen vacancies can be formed in theoxide semiconductor film.

When an impurity, e.g., hydrogen is contained in the oxide semiconductorfilm in which oxygen vacancies are generated by addition of impurityelements, hydrogen enters an oxygen vacant site and forms a donor levelin the vicinity of the conduction band. As a result, the oxidesemiconductor film has increased conductivity to be a conductor. Anoxide semiconductor film that has become a conductor can be referred toas an oxide conductor film. That is, it can be said that thesemiconductor layer 140 is formed of an oxide semiconductor and theconductive layer 400 is formed of an oxide conductor film. It can alsobe said that the conductive layer 400 is formed of an oxidesemiconductor film having high conductivity or a metal oxide film havinghigh conductivity.

Note that the insulating layer 180 preferably contains hydrogen. Sincethe conductive layer 400 is in contact with the insulating layer 180,hydrogen contained in the insulating layer 180 can be diffused into theoxide semiconductor film formed at the same time as the semiconductorlayer 140. As a result, impurities can be added to the oxidesemiconductor film formed at the same time as the semiconductor layer140; thus, the conductivity of the conductive layer 400 can beincreased.

In the above manner, the conductive layer 400 can be formed at the sametime as the semiconductor layer 140, and conductivity is given to theconductive layer 400 after the formation. Such a structure results in areduction in manufacturing costs.

Oxide semiconductor films generally have a visible light transmittingproperty because of their large energy gap. In contrast, an oxideconductor film is an oxide semiconductor film having a donor level inthe vicinity of the conduction band. Thus, the influence of lightabsorption due to the donor level is small, so that an oxide conductorfilm has a visible light transmitting property comparable to that of anoxide semiconductor film.

Thus, the conductive layer 190 and the conductive layer 400 have alight-transmitting property. Therefore, the capacitor 61 can have alight-transmitting property as a whole.

<Another Structure of Transmissive Liquid Crystal Panel>

A transmissive liquid crystal panel can have a peripheral portion invarious shapes and the protection film 23 corresponding to the shape ofthe peripheral portion as in a manner similar to that of a reflectiveliquid crystal panel.

FIG. 23, FIG. 24, and FIG. 25 are cross-sectional views of transmissiveliquid crystal panels. A transmissive liquid crystal panel of oneembodiment of the present invention can have a structure illustrated inFIG. 23 in which the peripheral portion does not have unevenness.Alternatively, a structure illustrated in FIG. 24 in which theprotection film 23 is hardly deposited on the rear surface of thedisplay device (a surface of the substrate 100 where the transistor 50and the liquid crystal element 81 are not formed) can be employed.Alternatively, a structure illustrated in FIG. 25 in which theprotection film 23 is deposited on neither a top surface of the displaydevice (a surface of the substrate 300 where the liquid crystal elementis not formed) nor the rear surface of the display device (the surfaceof the substrate 100 where the transistor 50 and the liquid crystalelement 81 are not formed) can be employed. Note that as illustrated inFIG. 24 and FIG. 25, the protection film 23 can cover edges of thesubstrate. Alternatively, a structure illustrated in FIG. 26 in whichthe protection film 23 is not deposited in the region 14 (the rearsurface and the side surface of the display device) can be employed.

The transmissive liquid crystal panel can be combined with a touchsensor to form a touch panel. FIG. 27, FIG. 28, and FIG. 29 arecross-sectional views of touch panels. FIG. 27 and FIG. 28 illustrateexamples of in-cell touch panels. In FIG. 27, the protection film 23 isdeposited in the whole region except for an FPC portion. In FIG. 28, theprotection film 23 is hardly deposited on the substrate 100 side. FIG.29 illustrates an example of an on-cell touch panel.

<Organic EL Panel>

The display device 10 including the light-emitting element 70 as adisplay element can be manufactured.

FIG. 30, FIG. 31, and FIG. 32 are cross-sectional views of displaydevices including a light-emitting element. Note that the samecomponents (e.g., transistors) used in the liquid crystal panel can beformed in the same manner as the liquid crystal panel.

<<Light-Emitting Element 70>>

As the light-emitting element 70, a self-luminous element can be used,and an element whose luminance is controlled by current or voltage isincluded in the category of the light-emitting element. For example, alight-emitting diode (LED), an organic EL element, an inorganic ELelement, or the like can be used. For example, an organic element whichincludes a lower electrode, an upper electrode, and a layer (alsoreferred to as an EL layer 250) containing a light-emitting organiccompound between the lower electrode and the upper electrode can be usedas the light-emitting element 70.

The light-emitting element may be a top emission, bottom emission, ordual emission light-emitting element. A conductive film that transmitsvisible light is used as the electrode through which light is extracted.A conductive film that reflects visible light is preferably used as theelectrode through which light is not extracted.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the lower electrode of the conductive layer220 and the upper electrode of the conductive layer 260, holes areinjected to the EL layer 250 from the anode side and electrons areinjected to the EL layer 250 from the cathode side. The injectedelectrons and holes recombine in the EL layer 250 and a light-emittingsubstance contained in the EL layer 250 emits light.

The EL layer 250 includes at least a light-emitting layer. In additionto the light-emitting layer, the EL layer 250 may further include one ormore layers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with a high electron- andhole-transport property), and the like.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer 250, and an inorganic compound may be used. Each of thelayers included in the EL layer 250 can be formed by any of thefollowing methods: an evaporation method (including a vacuum evaporationmethod), a transfer method, a printing method, an inkjet method, acoating method, and the like.

The light-emitting element may contain two or more kinds oflight-emitting substances. Thus, for example, a light-emitting elementthat emits white light can be achieved. For example, light-emittingsubstances are selected so that two or more light-emitting substancesemit complementary colors to obtain white light emission. Alight-emitting substance that emits red (R) light, green (G) light, blue(B) light, yellow (Y) light, or orange (0) light or a light-emittingsubstance that emits light containing spectral components of two or moreof R light, G light, and B light can be used, for example. Alight-emitting substance that emits blue light and a light-emittingsubstance that emits yellow light may be used, for example. At thistime, the emission spectrum of the light-emitting substance that emitsyellow light preferably contains spectral components of G light and Rlight. The emission spectrum of the light-emitting element 70 preferablyhas two or more peaks in the wavelength range in a visible region (e.g.,greater than or equal to 350 nm and less than or equal to 750 nm orgreater than or equal to 400 nm and less than or equal to 800 nm).

The EL layer 250 may include a plurality of light-emitting layers. Inthe EL layer 250, the plurality of light-emitting layers may be stackedin contact with one another or may be stacked with a separation layerprovided therebetween. The separation layer may be provided between afluorescent layer and a phosphorescent layer, for example.

The separation layer can be provided, for example, to prevent energytransfer by the Dexter mechanism (particularly triplet energy transfer)from a phosphorescent material or the like in an excited state which isgenerated in the phosphorescent layer to a fluorescent material or thelike in the fluorescent layer. The thickness of the separation layer maybe several nanometers. Specifically, the thickness of the separationlayer may be greater than or equal to 0.1 nm and less than or equal to20 nm, greater than or equal to 1 nm and less than or equal to 10 nm, orgreater than or equal to 1 nm and less than or equal to 5 nm. Theseparation layer contains a single material (preferably, a bipolarsubstance) or a plurality of materials (preferably, a hole-transportmaterial and an electron-transport material).

The separation layer may be formed using a material contained in alight-emitting layer in contact with the separation layer. Thisfacilitates the manufacture of the light-emitting element and reducesthe drive voltage. For example, in the case where the phosphorescentlayer contains a host material, an assist material, and thephosphorescent material (a guest material), the separation layer maycontain the host material and the assist material. In other words, theseparation layer includes a region not containing the phosphorescentmaterial and the phosphorescent layer includes a region containing thephosphorescent material in the above structure.

Accordingly, the separation layer and the phosphorescent layer can beevaporated separately depending on whether a phosphorescent material isused or not. With such a structure, the separation layer and thephosphorescent layer can be formed in the same chamber. Thus, themanufacturing cost can be reduced.

<Layer 230 for Adjusting Optical Path>

The light-emitting element 70 in FIG. 30 is an example of alight-emitting element having a microcavity structure. For example, themicrocavity structure may be formed using the lower electrode and theupper electrode of the light-emitting element 70 so that light with aspecific wavelength can be extracted from the light-emitting elementefficiently.

Specifically, a reflective film which reflects visible light is used asthe lower electrode, and a semi-transmissive and semi-reflective filmwhich transmits part of visible light and reflects part of visible lightis used as the upper electrode. The upper electrode and the lowerelectrode are arranged so that light with a specific wavelength can beextracted efficiently.

The lower electrode functions as, for example, a lower electrode or ananode of the light-emitting element. The lower electrode has a functionof adjusting the optical path length so that desired light emitted fromlight-emitting layers resonates and its wavelength can be amplified. Alayer 230 that adjusts the optical path length is not necessarilyprovided in the lower electrode. At least one layer included in thelight-emitting element can be used to adjust the optical path length.The layer 230 that adjusts the optical path length can be formed using,for example, indium oxide, indium tin oxide (ITO), indium zinc oxide,zinc oxide (ZnO), or zinc oxide to which gallium is added.

In the case of using the microcavity structure, a semi-transmissive andsemi-reflective electrode can be used as the upper electrode of thelight-emitting element. The semi-transmissive semi-reflective electrodeis formed using a reflective conductive material and alight-transmitting conductive material. As the conductive materials, aconductive material having a visible light reflectivity of higher thanor equal to 20% and lower than or equal to 80%, preferably higher thanor equal to 40% and lower than or equal to 70%, and a resistivity oflower than or equal to 1×10⁻² Ω·cm can be used. The semi-transmissivesemi-reflective electrode can be formed using one or more kinds ofconductive metals, conductive alloys, conductive compounds, and thelike. In particular, a material with a small work function (3.8 eV orless) is preferable. For example, aluminum, silver, an element belongingto Group 1 or 2 of the periodic table (e.g., an alkali metal such aslithium or cesium, an alkaline earth metal such as calcium or strontium,or magnesium), an alloy containing any of these elements (e.g., Ag—Mg orAl—Li), a rare earth metal such as europium or ytterbium, and an alloycontaining any of these rare earth metals.

The electrodes can each be formed by an evaporation method or asputtering method. Alternatively, a discharging method such as anink-jet method, a printing method such as a screen printing method, or aplating method may be used.

Note that an organic EL can employ a structure other than a microcavitystructure. For example, a separate coloring method by which differentcolors are emitted from light-emitting elements, or a white EL method inwhich a material emitting white light is used can be employed.

<<Partition Wall 245>>

An insulating material can be used for a partition wall 245. Forexample, an inorganic material, an organic material, or a stacked-layermaterial of an inorganic material and an organic material can be used.Specifically, a film containing silicon oxide, silicon nitride, or thelike, acrylic, polyimide, a photosensitive resin, or the like can beused.

<<Conductive Layer 200>>

The conductive layer 200 is formed using a metal element selected fromaluminum, chromium, copper, tantalum, titanium, molybdenum, nickel,iron, cobalt, and tungsten; an alloy containing any of these metalelements as a component; an alloy containing any of these metal elementsin combination; or the like. Further, one or more metal elementsselected from manganese and zirconium may be used. The conductive layer200 may have a single-layer structure or a layered structure of two ormore layers. For example, any of the following can be used: asingle-layer structure of an aluminum film containing silicon; asingle-layer structure of a copper film containing manganese; atwo-layer structure in which a titanium film is stacked over an aluminumfilm; a two-layer structure in which a titanium film is stacked over atitanium nitride film; a two-layer structure in which a tungsten film isstacked over a titanium nitride film; a two-layer structure in which atungsten film is stacked over a tantalum nitride film or a tungstennitride film; a two-layer structure in which a copper film is stackedover a copper film containing manganese; a three-layer structure inwhich a titanium film, an aluminum film, and a titanium film are stackedin this order; a three-layer structure in which a copper film containingmanganese, a copper film, and a copper film containing manganese arestacked in this order; and the like. Alternatively, an alloy film or anitride film which contains aluminum and one or more elements selectedfrom titanium, tantalum, tungsten, molybdenum, chromium, neodymium, andscandium may be used.

<<Insulating Layer 210>>

The insulating layer 210 has a function of making a flat surface. Aninorganic material or an organic material can be used for the insulatinglayer 210. For example, an oxide insulating film of silicon oxide,silicon oxynitride, aluminum oxide, aluminum oxynitride, gallium oxide,gallium oxynitride, yttrium oxide, yttrium oxynitride, hafnium oxide,hafnium oxynitride, or the like; a nitride insulating film of siliconnitride, aluminum nitride, or the like; or a heat-resistant organicmaterial such as a polyimide resin, an acrylic resin, a polyimide amideresin, a benzocyclobutene resin, a polyamide resin, or an epoxy resincan be used.

<Conductive Layer 260>

The conductive layer 260 that transmits visible light can be formedusing, for example, indium oxide, indium tin oxide (ITO), indium zincoxide, zinc oxide (ZnO), or zinc oxide to which gallium is added.Alternatively, a film of a metal material such as gold, silver,platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, palladium, or titanium; an alloy containing any of thesemetal materials; or a nitride of any of these metal materials (e.g.,titanium nitride) can be formed thin so as to have a light-transmittingproperty. A stack of any of the above materials can be used as theconductive layer. For example, a stacked film of ITO and an alloy ofsilver and magnesium is preferably used, in which case conductivity canbe increased. Further alternatively, graphene or the like may be used.

<Organic EL Panel Using Separate Coloring Method>

An organic EL element can be formed using a separate coloring method asillustrated in FIG. 31. FIG. 31 is different from FIG. 30 in that aseparate coloring method is used for the EL layer 250 over theconductive layer 220.

<Flexible Display Device>

The display device may be formed over a flexible substrate 101 or aflexible substrate 301 as illustrated in FIG. 32. The flexible substrateand the display device can be bonded to each other with the adhesivelayer 370. In this manner, a flexible touch panel that can be folded ora touch panel having a curved surface can be fabricated. Moreover, thethickness of the substrate can be small, leading to a reduction inweight of the touch panel.

<Manufacturing Method Example of Flexible Display Device>

Here, a method for manufacturing a flexible display device will bedescribed.

For convenience, a structure including a pixel and a circuit, astructure including an optical member such as a color filter, or astructure including a touch sensor is referred to as an element layer.An element layer includes a display element, for example, and mayinclude a wiring electrically connected to the display element or anelement such as a transistor used in a pixel or a circuit in addition tothe display element.

Here, a support body (e.g., the substrate 101 or the substrate 301) withan insulating surface where an element layer is formed is referred to asa base material.

As a method for forming an element layer over a flexible base materialprovided with an insulating surface, there are a method in which anelement layer is formed directly over the base material, and a method inwhich an element layer is formed over a supporting base material andthen the element layer is separated from the supporting base materialand transferred to the base material.

In the case where a material of the base material can withstand heatingtemperature in a process for forming the element layer, it is preferablethat the element layer be formed directly over the base material, inwhich case a manufacturing process can be simplified. At this time, theelement layer is preferably formed in a state where the base material isfixed to the supporting base material, in which case transfer thereof inan apparatus and between apparatuses can be easy.

In the case of employing the method in which the element layer is formedover the supporting base material and then transferred to the basematerial, first, a separation layer and an insulating layer are stackedover the supporting base material, and then the element layer is formedover the insulating layer. Next, the element layer is separated from thesupporting base material and then transferred to the base material. Atthis time, a material is selected that would causes separation at aninterface between the supporting base material and the separation layer,at an interface between the separation layer and the insulating layer,or in the separation layer.

For example, it is preferable that a stacked layer of a layer includinga high-melting-point metal material, such as tungsten, and a layerincluding an oxide of the metal material be used as the separationlayer; and a stacked layer of a plurality of layers, such as a siliconnitride layer and a silicon oxynitride layer be used over the separationlayer. The use of the high-melting-point metal material is preferablebecause the degree of freedom of the process for forming the elementlayer can be increased.

The separation may be performed by application of mechanical power, byetching of the separation layer, by dripping of a liquid into part ofthe separation interface to penetrate the entire separation interface,or the like. Alternatively, separation may be performed by heating theseparation interface by utilizing a difference in thermal expansioncoefficient.

The separation layer is unnecessary in the case where separation canoccur at an interface between the supporting base material and theinsulating layer. For example, glass is used as the supporting basematerial and an organic resin such as polyimide is used as theinsulating layer, a separation trigger is formed by locally heating partof the organic resin by laser light or the like, and separation isperformed at an interface between the glass and the insulating layer.Alternatively, a metal layer may be provided between the supporting basematerial and the insulating layer formed of an organic resin, andseparation may be performed at the interface between the metal layer andthe insulating layer by heating the metal layer by feeding a current tothe metal layer. In that case, the insulating layer formed of an organicresin can be used as a base material.

Examples of such a base material having flexibility include polyesterresins such as polyethylene terephthalate (PET) and polyethylenenaphthalate (PEN), a polyacrylonitrile resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, apolystyrene resin, a polyamide imide resin, and a polyvinyl chlorideresin. In particular, it is preferable to use a material with a lowthermal expansion coefficient, and for example, a polyamide imide resin,a polyimide resin, PET, or the like with a thermal expansion coefficientlower than or equal to 30×10⁻⁶/K can be suitably used. A substrate inwhich a fibrous body is impregnated with a resin (also referred to asprepreg) or a substrate whose thermal expansion coefficient is reducedby mixing an inorganic filler with an organic resin can also be used.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile elastic modulus or a fiber with a high Young'smodulus. Typical examples thereof include a polyvinyl alcohol basedfiber, a polyester based fiber, a polyamide based fiber, a polyethylenebased fiber, an aramid based fiber, a polyparaphenylene benzobisoxazolefiber, a glass fiber, and a carbon fiber. As the glass fiber, glassfiber using E glass, S glass, D glass, Q glass, or the like can be used.These fibers may be used in a state of a woven fabric or a nonwovenfabric, and a structure body in which this fibrous body is impregnatedwith a resin and the resin is cured may be used as the flexiblesubstrate. The structure body including the fibrous body and the resinis preferably used as the flexible substrate, in which case thereliability against bending or breaking due to local pressure can beincreased.

Alternatively, glass, metal, or the like that is thin enough to haveflexibility can be used as the base material. Alternatively, a compositematerial where glass and a resin material are attached to each other maybe used.

In the structure shown in FIG. 32, for example, a first separation layerand an insulating layer 112 are formed in this order over a firstsupporting base material, and then components in a layer over the firstseparation layer and the insulating layer 112 are formed. Separately, asecond separation layer and an insulating layer 312 are formed in thisorder over a second supporting base material, and then upper componentsare formed. Next, the first supporting base material is bonded to thesecond supporting base material with the adhesive layer 370. After that,separation at an interface between the second separation layer and theinsulating layer 312 is conducted so that the second supporting basematerial and the second separation layer are removed, and then thesubstrate 301 is bonded to the insulating layer 312 using an adhesivelayer 372. Furthermore, separation at an interface between the firstseparation layer and the insulating layer 112 is conducted so that thefirst supporting base material and the first separation layer areremoved, and then the substrate 101 is bonded to the insulating layer112 using an adhesive layer 371. Note that either side may be subjectedto separation and attachment first.

The above is the description of a manufacturing method of a flexibledisplay device.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 5

Described in Embodiment 5 is a modification example of the structure ofthe transistor described in Embodiment 4.

<<Stacked-Layer Oxide Semiconductor>>

In the semiconductor layer 140, a plurality of oxide semiconductor filmsthat differ in the atomic ratio of metal elements may be stacked. Forexample, in a transistor 51, oxide semiconductor layers 141 and 142 arestacked in this order over the insulating layer 130 as illustrated inFIG. 33A. Alternatively, the oxide semiconductor layer 142, the oxidesemiconductor layer 141, and an oxide semiconductor layer 143 arestacked in this order over the insulating layer 130 as illustrated inFIG. 33B. The oxide semiconductor layer 142 and the oxide semiconductorlayer 143 differ from the oxide semiconductor layer 141 in the atomicratio of metal elements.

<<Channel-Protective Transistor and Top-Gate Transistor>>

The transistor 50 illustrated in FIG. 12 is, but not limited to, abottom-gate transistor. FIG. 34A illustrates a transistor 53 and FIG.34B illustrates a transistor 54 as modification examples of thetransistor 50. Although the transistor 50 illustrated in FIG. 11B is achannel-etched transistor, it may be a channel-protective transistor(the transistor 53) including an insulating layer 165 as illustrated inthe cross-sectional view of FIG. 34A or may be a top-gate transistor(the transistor 54) as illustrated in the cross-sectional view of FIG.34B.

Note that all of transistors 52 included in the peripheral circuit (gatedriver and the like) may have the same structure or may have two or morekinds of structures. All of a plurality of transistors 50 included inthe pixel portion may have the same structure, or may have two or morekinds of structures.

Although an example of using a transistor including an oxidesemiconductor is shown in this embodiment, one embodiment of the presentinvention is not limited to this example. Depending on the case orcircumstances, a transistor including a semiconductor material that isnot an oxide semiconductor may be used in one embodiment of the presentinvention.

For example, a transistor in which a Group 14 element, a compoundsemiconductor, an oxide semiconductor, or the like is used for thesemiconductor layer 140 can be used. Specifically, a semiconductorcontaining silicon, a semiconductor containing gallium arsenide, anorganic semiconductor, or the like can be used.

For example, single crystal silicon, polysilicon, or amorphous siliconcan be used for the semiconductor layer of the transistor.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 6

In this embodiment, a structural example of the display panel of oneembodiment of the present invention will be described with reference toFIGS. 36A to 36C.

Structural Example

FIG. 36A is a top view of the display device of one embodiment of thepresent invention. FIG. 36B is a circuit diagram illustrating a pixelcircuit that can be used in the case where a liquid crystal element isused in a pixel in the display device of one embodiment of the presentinvention. FIG. 36C is a circuit diagram illustrating a pixel circuitthat can be used in the case where an organic EL element is used in apixel in the display device of one embodiment of the present invention.

The transistor in the pixel portion can be formed in accordance with theabove embodiments. The transistor can be easily formed as an n-channeltransistor, and thus part of a driver circuit that can be formed usingan n-channel transistor is formed over the same substrate as thetransistor of the pixel portion. With the use of any of the transistorsdescribed in the above embodiments for the pixel portion or the drivercircuit in this manner, a highly reliable display device can beprovided.

FIG. 36A illustrates an example of a top view of an active matrixdisplay device. A pixel portion 701, a scan line driver circuit 702, ascan line driver circuit 703, and a signal line driver circuit 704 areformed over a substrate 700 of the display device. In the pixel portion701, a plurality of signal lines extended from the signal line drivercircuit 704 are arranged and a plurality of scan lines extended from thescan line driver circuit 702 and the scan line driver circuit 703 arearranged. Note that pixels which include display elements are providedin a matrix in respective regions where the scan lines and the signallines intersect with each other. The substrate 700 of the display deviceis connected to a timing control circuit (also referred to as acontroller or a controller IC) through a connection portion such as aflexible printed circuit (FPC).

In FIG. 36A, the scan line driver circuit 702, the scan line drivercircuit 703, and the signal line driver circuit 704 are formed over thesubstrate 700 where the pixel portion 701 is formed. Accordingly, thenumber of components which are provided outside, such as a drivercircuit, can be reduced, so that a reduction in cost can be achieved.Furthermore, if the driver circuit is provided outside the substrate700, wirings would need to be extended and the number of wiringconnections would increase. When the driver circuit is provided over thesubstrate 700, the number of wiring connections can be reduced.Consequently, an improvement in reliability or yield can be achieved.

<Liquid Crystal Display Device>

FIG. 36B illustrates an example of a circuit configuration of the pixel.Here, a pixel circuit which is applicable to a pixel of a VA liquidcrystal display device is illustrated as an example.

This pixel circuit can be applied to a structure in which one pixelincludes a plurality of pixel electrode layers. The pixel electrodelayers are connected to different transistors, and the transistors canbe driven with different gate signals. Accordingly, signals applied toindividual pixel electrode layers in a multi-domain pixel can becontrolled independently.

A gate wiring 712 of a transistor 716 and a gate wiring 713 of atransistor 717 are separated so that different gate signals can besupplied thereto. In contrast, a data line 714 is shared by thetransistors 716 and 717. The transistor described in any of the aboveembodiments can be used as appropriate as each of the transistors 716and 717. Thus, a highly reliable liquid crystal display device can beprovided.

A first pixel electrode layer is electrically connected to thetransistor 716 and a second pixel electrode layer is electricallyconnected to the transistor 717. The first pixel electrode and thesecond pixel electrode are separated. Shapes of the first pixelelectrode and the second pixel electrode are not especially limited. Forexample, the first pixel electrode may have a V-like shape.

A gate electrode of the transistor 716 is connected to the gate wiring712, and a gate electrode of the transistor 717 is connected to the gatewiring 713. When different gate signals are supplied to the gate wiring712 and the gate wiring 713, operation timings of the transistor 716 andthe transistor 717 can be varied. As a result, alignment of liquidcrystals can be controlled.

Furthermore, storage capacitors may be formed using a capacitor wiring710, gate insulating films functioning as dielectrics, and capacitorelectrodes electrically connected to the first pixel electrode layer andthe second pixel electrode layer.

The multi-domain pixel includes a first liquid crystal element 718 and asecond liquid crystal element 719. The first liquid crystal element 718includes the first pixel electrode layer, a counter electrode layer, anda liquid crystal layer therebetween. The second liquid crystal element719 includes the second pixel electrode layer, a counter electrodelayer, and a liquid crystal layer therebetween.

Note that a pixel circuit of the present invention is not limited tothat shown in FIG. 36B. For example, a switch, a resistor, a capacitor,a transistor, a sensor, a logic circuit, or the like may be added to thepixel circuit illustrated in FIG. 36B.

<Organic EL Display Device>

FIG. 36C illustrates another example of a circuit configuration of thepixel. Here, a pixel structure of a display device using an organic ELelement is shown.

In an organic EL element, by application of voltage to a light-emittingelement, electrons are injected from one of a pair of electrodes andholes are injected from the other of the pair of electrodes, into alayer containing a light-emitting organic compound; thus, current flows.The electrons and holes are recombined, and thus, the light-emittingorganic compound is excited. The light-emitting organic compound returnsto a ground state from the excited state, thereby emitting light. Owingto such a mechanism, this light-emitting element is referred to as acurrent-excitation light-emitting element.

FIG. 36C illustrates an applicable example of a pixel circuit. Here, onepixel includes two n-channel transistors. Note that a metal oxide filmof one embodiment of the present invention can be used for a channelformation region of the n-channel transistor. Further, digital timegrayscale driving can be employed for the pixel circuit.

The configuration of the applicable pixel circuit and operation of apixel employing digital time grayscale driving will be described.

A pixel 720 includes a switching transistor 721, a driver transistor722, a light-emitting element 724, and a capacitor 723. A gate electrodelayer of the switching transistor 721 is connected to a scan line 726, afirst electrode (one of a source electrode layer and a drain electrodelayer) of the switching transistor 721 is connected to a signal line725, and a second electrode (the other of the source electrode layer andthe drain electrode layer) of the switching transistor 721 is connectedto a gate electrode layer of the driver transistor 722. The gateelectrode layer of the driver transistor 722 is connected to a powersupply line 727 through the capacitor 723, a first electrode of thedriver transistor 722 is connected to the power supply line 727, and asecond electrode of the driver transistor 722 is connected to a firstelectrode (a pixel electrode) of the light-emitting element 724. Asecond electrode of the light-emitting element 724 corresponds to acommon electrode 728. The common electrode 728 is electrically connectedto a common potential line formed over the same substrate as the commonelectrode 728.

As the switching transistor 721 and the driver transistor 722, any ofthe transistors described in other embodiments can be used asappropriate. In this manner, a highly reliable organic EL display devicecan be provided.

The potential of the second electrode (the common electrode 728) of thelight-emitting element 724 is set to be a low power supply potential.Note that the low power supply potential is lower than a high powersupply potential supplied to the power supply line 727. For example, thelow power supply potential can be GND, 0 V, or the like. The high powersupply potential and the low power supply potential are set to be higherthan or equal to the forward threshold voltage of the light-emittingelement 724, and the difference between the potentials is applied to thelight-emitting element 724, whereby current is supplied to thelight-emitting element 724, leading to light emission. The forwardvoltage of the light-emitting element 724 refers to a voltage at which adesired luminance is obtained, and includes at least a forward thresholdvoltage.

Note that the gate capacitance of the driver transistor 722 may be usedas a substitute for the capacitor 723, so that the capacitor 723 can beomitted. The gate capacitance of the driver transistor 722 may be formedbetween the channel formation region and the gate electrode layer.

Next, a signal input to the driver transistor 722 will be described. Inthe case of a voltage-input voltage driving method, a video signal forsufficiently turning on or off the driver transistor 722 is input to thedriver transistor 722. In order for the driver transistor 722 to operatein a linear region, voltage higher than the voltage of the power supplyline 727 is applied to the gate electrode layer of the driver transistor722. Note that voltage higher than or equal to voltage which is the sumof power supply line voltage and the threshold voltage V_(th) of thedriver transistor 722 is applied to the signal line 725.

In the case of performing analog grayscale driving, a voltage higherthan or equal to a voltage which is the sum of the forward voltage ofthe light-emitting element 724 and the threshold voltage V_(th) of thedriver transistor 722 is applied to the gate electrode layer of thedriver transistor 722. A video signal by which the driver transistor 722is operated in a saturation region is input, so that current is suppliedto the light-emitting element 724. In order for the driver transistor722 to operate in a saturation region, the potential of the power supplyline 727 is set higher than the gate potential of the driver transistor722. When an analog video signal is used, it is possible to supplycurrent to the light-emitting element 724 in accordance with the videosignal and perform analog grayscale driving.

Note that the configuration of the pixel circuit of the presentinvention is not limited to that shown in FIG. 36C. For example, aswitch, a resistor, a capacitor, a sensor, a transistor, a logiccircuit, or the like may be added to the pixel circuit illustrated inFIG. 36C.

In the case where the transistor shown in the above embodiments is usedfor the circuit shown in FIGS. 36A to 36C, the source electrode (thefirst electrode) is electrically connected to the low potential side andthe drain electrode (the second electrode) is electrically connected tothe high potential side. Furthermore, the potential of the first gateelectrode may be controlled by a control circuit or the like and thepotential described above as an example, e.g., a potential lower thanthe potential applied to the source electrode, may be input to thesecond gate electrode through a wiring that is not illustrated.

For example, in this specification and the like, for example, a displayelement, a display device which is a device including a display element,a light-emitting element, and a light-emitting device which is a deviceincluding a light-emitting element can employ a variety of modes or caninclude a variety of elements. The display element, the display device,the light-emitting element, or the light-emitting device includes atleast one of an electroluminescence (EL) element (e.g., an EL elementincluding organic and inorganic materials, an organic EL element, or aninorganic EL element), an LED (e.g., a white LED, a red LED, a greenLED, or a blue LED), a transistor (a transistor that emits lightdepending on current), an electron emitter, a liquid crystal element,electronic ink, an electrophoretic element, a grating light valve (GLV),a plasma display panel (PDP), a display element using micro electromechanical systems (MEMS), a digital micromirror device (DMD), a digitalmicro shutter (DMS), MIRASOL (registered trademark), an interferometricmodulator display (IMOD) element, a MEMS shutter display element, anoptical-interference-type MEMS display element, an electrowettingelement, a piezoelectric ceramic display, a display element including acarbon nanotube, and the like. Other than the above, a display mediumwhose contrast, luminance, reflectance, transmittance, or the like ischanged by an electrical or magnetic effect may be included. Note thatexamples of a display device including an EL element include an ELdisplay. Examples of a display device including an electron emitterinclude a field emission display (FED) and an SED-type flat paneldisplay (SED: surface-conduction electron-emitter display). Examples ofa display device including a liquid crystal element include a liquidcrystal display (e.g., a transmissive liquid crystal display, atransflective liquid crystal display, a reflective liquid crystaldisplay, a direct-view liquid crystal display, or a projection liquidcrystal display). Examples of a display device including electronic ink,Electronic Liquid Powder (registered trademark), or an electrophoreticelement include electronic paper. In the case of a transflective liquidcrystal display or a reflective liquid crystal display, some or all ofpixel electrodes function as reflective electrodes. For example, some orall of pixel electrodes are formed to contain aluminum, silver, or thelike. In such a case, a memory circuit such as an SRAM can be providedunder the reflective electrodes, leading to lower power consumption.Note that in the case of using an LED, graphene or graphite may beprovided under an electrode or a nitride semiconductor of the LED.Graphene or graphite may be a multilayer film in which a plurality oflayers are stacked. As described above, provision of graphene orgraphite enables easy formation of a nitride semiconductor thereover,such as an n-type GaN semiconductor layer including crystals.Furthermore, a p-type GaN semiconductor layer including crystals or thelike can be provided thereover, and thus the LED can be formed. Notethat an MN layer may be provided between the n-type GaN semiconductorlayer including crystals and graphene or graphite. The GaN semiconductorlayers included in the LED may be formed by MOCVD. Note that when thegraphene is provided, the GaN semiconductor layers included in the LEDcan also be formed by a sputtering method.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 7

In this embodiment, a structural example of the touch panel of oneembodiment of the present invention is described with reference to FIG.37.

<<Positional Relation Between Transistor and Wirings of Touch Sensor>>

FIG. 37 is a top view illustrating the positional relation between thepixel, a transistor, and wirings of the touch sensor. The conductivelayer 410, which is an electrode for the touch sensor, can be providedso as to overlap with a source line 91 or a gate line 92, or can beprovided not to overlap with and parallel to the source line 91 or thegate line 92, for example. The conductive layer 410, which is a wiringof the touch sensor, may overlap with a transistor 50 and a capacitor 61unlike in the example. Although the conductive layer 410 is provided notto overlap with the pixel 24, the conductive layer 410 can be providedto overlap with the pixel 24. The conductive layers 430 and 380 whichcan function as an electrode of the touch sensor can be arranged in asimilar manner.

<Structural Example of Sensor Electrode and the Like>

More specific structural examples of an input device 90, which functionsas a touch sensor, are described below with reference to drawings.

FIG. 38A is a top view of the input device 90. The input device 90includes a plurality of electrodes 931, a plurality of electrodes 932, aplurality of wirings 941, and a plurality of wirings 942 over asubstrate 930. The substrate 930 is provided with an FPC 950 which iselectrically connected to each of the plurality of wirings 941 and theplurality of wirings 942. FIG. 38A illustrates an example in which theFPC 950 is provided with an IC 951.

FIG. 38B shows an enlarged view of a region surrounded by a dasheddotted line in FIG. 38A. The electrodes 931 are each in the form of aseries of rhombic electrode patterns aligned in a lateral direction ofthis figure. The rhombic electrode patterns aligned in a line areelectrically connected to each other. The electrodes 932 are also eachin the form of a series of rhombic electrode patterns aligned in alongitudinal direction of this figure and the rhombic electrode patternsaligned in a line are electrically connected. Part of the electrode 931and part of the electrode 932 overlap and intersect with each other. Atthis intersection portion, an insulator is sandwiched in order to avoidan electrical short-circuit between the electrode 931 and the electrode932.

As shown in FIG. 38C, the electrodes 932 may form a plurality ofisland-shape rhombic electrodes 933 and bridge electrodes 934. Theelectrodes 933 are aligned in a longitudinal direction of this figure,and two adjacent electrodes 933 are electrically connected to each otherby the bridge electrode 934. Such a structure makes it possible that theelectrodes 933 and the electrodes 931 can be formed at the same time byprocessing the same conductive film. This can prevent variations in thethickness of these films, and can prevent the resistance value and thelight transmittance of each electrode from varying from place to place.Note that although the electrodes 932 include the bridge electrodes 934here, the electrodes 931 may have such a structure.

As shown in FIG. 38D, a design in which rhombic electrode patterns ofthe electrodes 931 and 932 shown in FIG. 38B are hollowed out and onlyedge portions are left may be used. At that time, when the electrodes931 and the electrodes 932 are too small in width for the users to view,the electrodes 931 and the electrodes 932 can be formed using alight-blocking material such as a metal or an alloy, as described later.In addition, either the electrodes 931 or the electrodes 932 shown inFIG. 38D may include the above bridge electrodes 934.

One of the electrodes 931 is electrically connected to one of thewirings 941. One of the electrodes 932 is electrically connected to oneof the wirings 942. Here, one of the electrodes 931 and 932 correspondsto a row wiring, and the other corresponds to a column wiring.

As examples, enlarged schematic views of part of the electrodes 931 orthe electrodes 932 are shown in FIGS. 39A to 39D. The electrodes canhave various shapes.

FIGS. 40A to 40C illustrate examples of the case where electrodes 936and electrodes 937, which have a top surface shape of thin lines, areused instead of the electrodes 931 and the electrodes 932. FIG. 40Ashows an example in which linear electrodes 936 and 937 are arranged soas to form a lattice shape. In FIGS. 40B and 40C, the electrodes 936 and937 having a zigzag shape are arranged.

FIGS. 41A to 41C show enlarged views of a region surrounded by a dasheddotted line in FIG. 40B, and FIGS. 41D to 41F show enlarged views of aregion surrounded by a dashed dotted line in FIG. 41C. In thesedrawings, the electrodes 936, the electrodes 937, and intersectionportions 938 at which the electrodes 936 and the electrodes 937intersect are illustrated. The straight-line portions of the electrodes936 and the electrodes 937 shown in FIGS. 41A and 41D may have aserpentine shape that meanders with angled corners as shown in FIGS. 41Band 41E or may have a serpentine shape that continuously meanders asshown in FIGS. 41C and 41F.

<Structural Example of in-Cell Touch Panel>

A structural example of a touch panel incorporating the touch sensorinto a display portion including a plurality of pixels will be describedbelow. Here, an example where a liquid crystal element is used as adisplay element provided in the pixel is shown.

FIG. 42A is an equivalent circuit diagram of part of a pixel circuitprovided in the display portion of the touch panel exemplified in thisstructural example.

Each pixel includes at least a transistor 3503 and a liquid crystalelement 3504. In addition, a gate of the transistor 3503 is electricallyconnected to a wiring 3501 and one of a source and a drain of thetransistor 3503 is electrically connected to a wiring 3502.

The pixel circuit includes a plurality of wirings extending in the Xdirection (e.g., a wiring 3510_1 and a wiring 3510_2) and a plurality ofwirings extending in the Y direction (e.g., a wiring 3511). They areprovided to intersect with each other, and capacitance is formedtherebetween.

Among the pixels provided in the pixel circuit, electrodes of the liquidcrystal elements of some pixels adjacent to each other are electricallyconnected to each other to form one block. The block is classified intotwo types: an island-shaped block (e.g., a block 3515_1 or a block3515_2) and a linear block (e.g., a block 3516) extending in the Ydirection. Note that only part of the pixel circuit is illustrated inFIGS. 42A and 42B, and actually, these two kinds of blocks arerepeatedly arranged in the X direction and the Y direction.

The wiring 3510_1 (or the wiring 3510_2) extending in the X direction iselectrically connected to the island-shaped block 3515_1 (or the block3515_2). Although not illustrated, the wiring 3510_1 extending in the Xdirection is electrically connected to a plurality of island-shapedblocks 3515_1 which are provided discontinuously along the X directionwith the linear blocks therebetween. Furthermore, the wiring 3511extending in the Y direction is electrically connected to the linearblock 3516.

FIG. 42B is an equivalent circuit diagram illustrating the connectionbetween a plurality of wirings 3510 extending in the X direction and theplurality of wirings 3511 extending in the Y direction. Input voltage ora common potential can be input to each of the wirings 3510 extending inthe X direction. Furthermore, a ground potential can be input to each ofthe wirings 3511 extending in the Y direction, or each of the wirings3511 can be electrically connected to a detection circuit.

Operation of the above-described touch panel will be described belowwith reference to FIGS. 43A and 43B.

Here, one frame period is divided into a writing period and a sensingperiod. The writing period is a period in which image data is written toa pixel, and the wirings 3510 (also referred to as gate lines) aresequentially selected. On the other hand, the sensing period is a periodin which sensing is performed by a touch sensor, and the wirings 3510extending in the X direction are sequentially selected and input voltageis input.

FIG. 43A is an equivalent circuit diagram in the writing period. In thewiring period, a common potential is input to both the wiring 3510extending in the X direction and the wiring 3511 extending in the Ydirection.

FIG. 43B is an equivalent circuit diagram at some point in time in thesensing period. In the sensing period, each of the wirings 3511extending in the Y direction is electrically connected to the detectioncircuit. Input voltage is input to the wirings 3510 extending in the Xdirection which are selected, and a common potential is input to thewirings 3510 extending in the X direction which are not selected.

Note that the driving method described here can be applied to not onlyan in-cell touch panel but also the above-described touch panels, andcan be used in combination with the method described in the drivingmethod example.

It is preferable that a period in which an image is written and a periodin which sensing is performed by a touch sensor be separately providedas described above. Thus, a decrease in sensitivity of the touch sensorcaused by noise generated when data is written to a pixel can besuppressed.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 8

In this embodiment, a structure of an oxide semiconductor film isdescribed.

<<Film Formation Method>>

An example of a method for forming a CAAC-OS film is described below.

FIG. 44A is a schematic view of the inside of a film formation chamber.The CAAC-OS film can be formed by a sputtering method.

As shown in FIG. 44A, a substrate 5220 and a target 5230 are arranged toface each other. Plasma 5240 is generated between the substrate 5220 andthe target 5230. A heating mechanism 5260 is under the substrate 5220.The target 5230 is attached to a backing plate (not illustrated in thedrawing). A plurality of magnets is arranged to face the target 5230with the backing plate positioned therebetween. A sputtering method inwhich the disposition speed is increased by utilizing a magnetic fieldof the magnets is referred to as a magnetron sputtering method.

The distance d between the substrate 5220 and the target 5230 (alsoreferred to as a target-substrate distance (T-S distance)) is greaterthan or equal to 0.01 m and less than or equal to 1 m, preferablygreater than or equal to 0.02 m and less than or equal to 0.5 m. Thefilm formation chamber is mostly filled with a deposition gas (e.g., anoxygen gas, an argon gas, or a mixed gas containing oxygen at 5 vol % orhigher) and the pressure in the film formation chamber is controlled tobe higher than or equal to 0.01 Pa and lower than or equal to 100 Pa,preferably higher than or equal to 0.1 Pa and lower than or equal to 10Pa. Here, discharge starts by application of a voltage at a certainvalue or higher to the target 5230, and the plasma 5240 is observed. Themagnetic field forms a high-density plasma region in the vicinity of thetarget 5230. In the high-density plasma region, the deposition gas isionized, so that an ion 5201 is generated. Examples of the ion 5201include an oxygen cation (O⁺) and an argon cation (Ar⁺).

Here, the target 5230 has a polycrystalline structure which includes aplurality of crystal grains and in which a cleavage plane exists in anyof the crystal grains. As an example, a crystal structure of InMZnO₄(the element M is aluminum, gallium, yttrium, or tin, for example)included in the target 5230 is illustrated in FIG. 45. Note that FIG. 45illustrates the crystal structure of InMZnO₄ observed from a directionparallel to a b-axis. In the crystal of InMZnO₄, oxygen atoms arenegatively charged, whereby repulsive force is generated between the twoadjacent M-Zn—O layers. Thus, the InMZnO₄ crystal has a cleavage planebetween the two adjacent M-Zn—O layers.

The ion 5201 generated in the high-density plasma region is acceleratedtoward the target 5230 side by an electric field, and then collides withthe target 5230. At this time, a pellet 5200 which is a flat-plate-likeor pellet-like sputtered particles is separated from the cleavage plane(FIG. 44A). The pellet 5200 is between the two cleavage planes shown inFIG. 45. Thus, when the pellet 5200 is observed, the cross-sectionthereof is as shown in FIG. 44B, and the top surface thereof is as shownin FIG. 44C. Note that the structure of the pellet 5200 may be distortedby an impact of collision of the ion 5201. Note that along with theseparation of the pellet 5200, a particle 5203 is also sputtered fromthe target 5230. The particle 5203 has an atom or an aggregate ofseveral atoms. Therefore, the particle 5203 can be referred to as anatomic particle.

The pellet 5200 is a flat-plate-like (pellet-like) sputtered particlehaving a triangle plane, e.g., regular triangle plane. Alternatively,the pellet 5200 is a flat-plate-like (pellet-like) sputtered particlehaving a hexagon plane, e.g., regular hexagon plane. However, the shapeof a flat plane of the pellet 5200 is not limited to a triangle or ahexagon. For example, the flat plane may have a shape formed bycombining two or more triangles. For example, a quadrangle (e.g.,rhombus) may be formed by combining two triangles (e.g., regulartriangles).

The thickness of the pellet 5200 is determined depending on the kind ofthe deposition gas and the like. For example, the thickness of thepellet 5200 is greater than or equal to 0.4 nm and less than or equal to1 nm, preferably greater than or equal to 0.6 nm and less than or equalto 0.8 nm In addition, for example, the width of the pellet 5200 isgreater than or equal to 1 nm and less than or equal to 3 nm, preferablygreater than or equal to 1.2 nm and less than or equal to 2.5 nm. Forexample, the ion 5201 collides with the target 5230 including theIn-M-Zn oxide. Then, the pellet 5200 including three layers of an M-Zn—Olayer, an In—O layer, and an M-Zn—O layer is separated. Note that theparticle 5203 is also sputtered from the target 5230 along with theseparation of the pellet 5200. The particle 5203 has an atom or anaggregate of several atoms. Therefore, the particle 5203 can be referredto as an atomic particle.

The pellet 5200 may receive a charge when passing through the plasma5240, so that surfaces thereof are negatively or positively charged. Forexample, the pellet 5200 receives a negative charge from O²⁻ in theplasma 5240. As a result, oxygen atoms on the surfaces of the pellet5200 may be negatively charged. In addition, when passing through theplasma 5240, the pellet 5200 is sometimes combined with indium, theelement M, zinc, oxygen, or the like in the plasma 5240 to grow up.

The pellet 5200 and the particle 5203 that have passed through theplasma 5240 reach a surface of the substrate 5220. Note that part of theparticles 5203 is discharged to the outside by a vacuum pump or the likebecause the particle 5203 is small in mass.

Next, deposition of the pellet 5200 and the particle 5203 on the surfaceof the substrate 5220 is described with reference to FIGS. 46A to 46E.

First, a first of the pellets 5200 is deposited over the substrate 5220.Since the pellet 5200 has a flat-plate-like shape, it is deposited sothat the flat plane faces to the surface of the substrate 5220 (FIG.46A). Here, a charge on a surface of the pellet 5200 on the substrate5220 side is lost through the substrate 5220.

Next, a second of the pellets 5200 reaches the substrate 5220. Here,since another surface of the first of the pellets 5200 and surfaces ofthe second of the pellets 5200 are charged, they repel each other (FIG.46B).

As a result, the second of the pellets 5200 avoids being deposited overthe first of the pellets 5200, and is deposited over the surface of thesubstrate 5220 so as to be a little distance away from the first of thepellets 5200 (FIG. 46C). With repetition of this, millions of thepellets 5200 are deposited over the surface of the substrate 5220 tohave a thickness of one layer. A region where any pellet 5200 is notdeposited is generated between adjacent pellets 5200.

Next, the particle 5203 reaches the surface of the substrate 5220 (FIG.46D).

The particle 5203 cannot be deposited over an active region such as thesurface of the pellet 5200. Therefore, the particle 5203 is deposited soas to fill a region where the pellets 5200 are not deposited. Theparticles 5203 grow in the horizontal (lateral) direction between thepellets 5200, thereby connecting the pellets 5200. In this way, theparticles 5203 are deposited until they fill regions where the pellets5200 are not deposited. This mechanism is similar to a depositionmechanism of the ALD method.

Note that there can be several mechanisms for the lateral growth of theparticles 5203 between the pellets 5200. For example, as shown in FIG.46E, the pellets 5200 can be connected from side surfaces of the firstM-Zn—O layers. In this case, after the first M-Zn—O layers makeconnection, the In—O layers and the second M-Zn—O layers are connectedin this order (the first mechanism).

Alternatively, as shown in FIG. 47A, first, the particles 5203 areconnected to the sides of the first M-Zn—O layers so that each side ofthe first M-Zn—O layer has one particle 5203. Then, as shown in FIG.47B, the particle 5203 is connected to each side of the In—O layers.After that, as shown in FIG. 47C, the particle 5203 is connected to eachside of the second M-Zn—O layers (the second mechanism). Note that theconnection can also be made by the simultaneous occurrence of thedeposition in FIGS. 47A, 47B, and 47C (the third mechanism).

As shown in the above, the above three mechanisms are considered as themechanisms of the lateral growth of the particles 5203 between thepellets 5200. However, the particles 5203 may grow up laterally betweenthe pellets 5200 by other mechanisms.

Therefore, even when the orientations of a plurality of pellets 5200 aredifferent from each other, generation of crystal boundaries can besuppressed since the particles 5203 laterally grow to fill gaps betweenthe plurality of pellets 5200. In addition, as the particles 5203 makesmooth connection between the plurality of pellets 5200, a crystalstructure different from a single crystal and a polycrystal is formed.In other words, a crystal structure including distortion between minutecrystal regions (pellets 5200) is formed. The regions filling the gapsbetween the crystal regions are distorted crystal regions; and thus, itwill be not appropriate to say that the regions have an amorphousstructure.

When the particles 5203 completely fill the regions between the pellets5200, a first layer with a thickness almost the same as that of thepellet 5200 is formed. Then, a new first of the pellets 5200 isdeposited over the first layer, and a second layer is formed. Withrepetition of this cycle, the stacked-layer thin film structure isformed (FIG. 44D).

A deposition way of the pellets 5200 changes depending on the surfacetemperature of the substrate 5220 or the like. For example, if thesurface temperature of the substrate 5220 is high, migration of thepellets 5200 occurs over the substrate 5220. As a result, a proportionof the pellets 5200 that are directly connected with each other withoutthe particles 5203 increases, whereby a CAAC-OS with high orientation ismade. The surface temperature of the substrate 5220 for formation of theCAAC-OS is higher than or equal to 100° C. and less than 500° C.,preferably higher than or equal to 140° C. and less than 450° C., orfurther preferably higher than or equal to 170° C. and less than 400° C.Therefore, even when a large-sized substrate of the 8th generation ormore is used as the substrate 5220, a warp or the like hardly occur.

On the other hand, if the surface temperature of the substrate 5220 islow, the migration of the pellets 5200 over the substrate 5220 does noteasily occur. As a result, the pellets 5200 are stacked to form ananocrystalline oxide semiconductor (nc-OS) or the like with loworientation (FIG. 48). In the nc-OS, the pellets 5200 are possiblydeposited with certain gaps since the pellets 5200 are negativelycharged. Therefore, the nc-OS film has low orientation but someregularity, and thus it has a denser structure than an amorphous oxidesemiconductor.

When spaces between the pellets are extremely small in a CAAC-OS, thepellets may form a large pellet. The inside of the large pellet has asingle crystal structure. For example, the size of the pellet may begreater than or equal to 10 nm and less than or equal to 200 nm, greaterthan or equal to 15 nm and less than or equal to 100 nm, or greater thanor equal to 20 nm and less than or equal to 50 nm, when seen from theabove.

According to such a model, the pellets 5200 are considered to bedeposited on the substrate 5220. A CAAC-OS can be deposited even when aformation surface does not have a crystal structure; therefore, a growthmechanism in this case is different from epitaxial growth. In addition,a uniform film of a CAAC-OS or an nc-OS can be formed even over alarge-sized glass substrate or the like. For example, even when thesurface of the substrate 5220 (formation surface) has an amorphousstructure (e.g., such as amorphous silicon oxide), a CAAC-OS can beformed.

In addition, even when the surface of the substrate 5220 (formationsurface) has an uneven shape, the pellets 5200 are aligned along theshape.

Embodiment 9 <Module>

A display module using a semiconductor device of one embodiment of thepresent invention is described below with reference to FIG. 49.

In a display module 8000 in FIG. 49, a touch sensor portion 8004connected to an FPC 8003, a display device 8006 connected to an FPC8005, a backlight unit 8007, a frame 8009, a printed board 8010, and abattery 8011 are provided between an upper cover 8001 and a lower cover8002. The backlight unit 8007, the battery 8011, the touch sensor 8004,or the like is not provided in some cases.

The semiconductor device of one embodiment of the present invention canbe used for, for example, the display device 8006.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the sizes of the touchsensor 8004 and the display device 8006.

The touch sensor 8004 can be a resistive touch sensor or a capacitivetouch sensor and can be formed to overlap with the display device 8006.A counter substrate (sealing substrate) of the display device 8006 canhave a touch panel function. A photosensor may be provided in each pixelof the display device 8006 to form an optical touch panel. An electrodefor a touch sensor may be provided in each pixel of the display device8006 to form a capacitive touch panel.

The backlight unit 8007 includes a light source 8008. The light source8008 may be provided at an end portion of the backlight unit 8007 and alight diffusing plate may be used.

The frame 8009 protects the display device 8006 and may also function asan electromagnetic shield for blocking electromagnetic waves generatedby the operation of the printed board 8010. The frame 8009 may functionas a radiator plate.

The printed board 8010 has a power supply circuit and a signalprocessing circuit for outputting a video signal and a clock signal. Asa power source for supplying power to the power supply circuit, anexternal commercial power source or a power source using the battery8011 provided separately may be used. The battery 8011 can be omitted inthe case of using a commercial power source.

The display module 8000 may be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

Embodiment 10 <Electronic Device>

In this embodiment, examples of an electronic device to which thedisplay device of one embodiment of the present invention can be appliedwill be described with reference to FIGS. 50A to 50F and FIGS. 51A to51D.

Examples of an electronic device including the display device includetelevision sets (also referred to as televisions or televisionreceivers), monitors of computers or the like, cameras such as digitalcameras or digital video cameras, digital photo frames, mobile phones(also referred to as cellular phones or mobile phone devices), portablegame machines, portable information terminals, audio reproducingdevices, and large game machines such as pachinko machines. Specificexamples of these electronic devices are illustrated in FIGS. 50A to 50Fand FIGS. 51A to 51D.

FIG. 50A illustrates a portable game machine including a housing 7101, ahousing 7102, a display portion 7103, a display portion 7104, amicrophone 7105, speakers 7106, an operation key 7107, a stylus 7108,and the like. The display device of one embodiment of the presentinvention can be used for the display portion 7103 or the displayportion 7104. When the display device of one embodiment of the presentinvention is used as the display portion 7103 or 7104, it is possible toprovide a user-friendly portable game machine with quality that hardlydeteriorates. Although the portable game machine illustrated in FIG. 50Aincludes two display portions, the display portion 7103 and the displayportion 7104, the number of display portions included in the portablegame machine is not limited to two.

FIG. 50B illustrates a smart watch, which includes a housing 7302, adisplay portion 7304, operation buttons 7311 and 7312, a connectionterminal 7313, a band 7321, a clasp 7322, and the like. The displaydevice or touch panel of one embodiment of the present invention can beused for the display portion 7304.

FIG. 50C illustrates a portable information terminal that includes adisplay portion 7502 incorporated in a housing 7501, operation buttons7503, an external connection port 7504, a speaker 7505, a microphone7506, and the like. The display device of one embodiment of the presentinvention can be used for the display portion 7502. Note that thedisplay portion 7502 is small- or medium-sized but can perform 8 kdisplay because it has greatly high definition; therefore, asignificantly clear image can be obtained.

FIG. 50D illustrates a video camera, which includes a first housing7701, a second housing 7702, a display portion 7703, operation keys7704, a lens 7705, a joint 7706, and the like. The operation keys 7704and the lens 7705 are provided for the first housing 7701, and thedisplay portion 7703 is provided for the second housing 7702. The firsthousing 7701 and the second housing 7702 are connected to each otherwith the joint 7706, and the angle between the first housing 7701 andthe second housing 7702 can be changed with the joint 7706. Imagesdisplayed on the display portion 7703 may be switched in accordance withthe angle at the joint 7706 between the first housing 7701 and thesecond housing 7702. The imaging device in one embodiment of the presentinvention can be provided in a focus position of the lens 7705. Thedisplay device of one embodiment of the present invention can be usedfor the image display portion 7703.

FIG. 50E illustrates a curved display including a display portion 7802incorporated in a housing 7801, an operation button 7803, a speaker7804, and the like. The display device of one embodiment of the presentinvention can be used for the display portion 7802.

FIG. 50F illustrates a digital signage including a display portion 7922provided on a utility pole 7921. The display device of one embodiment ofthe present invention can be used for the display portion 7922.

FIG. 51A illustrates a notebook personal computer, which includes ahousing 8121, a display portion 8122, a keyboard 8123, a pointing device8124, and the like. The display device of one embodiment of the presentinvention can be used for the display portion 8122. Note that thedisplay portion 8122 is small- or medium-sized but can perform 8 kdisplay because it has greatly high definition; therefore, asignificantly clear image can be obtained.

FIG. 51B is an external view of an automobile 9700. FIG. 51C illustratesa driver's seat of the automobile 9700. The automobile 9700 includes acar body 9701, wheels 9702, a dashboard 9703, lights 9704, and the like.The display device or input/output device of one embodiment of thepresent invention can be used in a display portion or the like of theautomobile 9700. For example, the display device, input/output device,or touch panel of one embodiment of the present invention can be used indisplay portions 9710 to 9715 illustrated in FIG. 51C.

The display portion 9710 and the display portion 9711 are each a displaydevice or an input/output device provided in an automobile windshield.The display device or input/output device of one embodiment of thepresent invention can be a see-through display device or input/outputdevice, through which the opposite side can be seen, using alight-transmitting conductive material for its electrodes. Such asee-through display device or input/output device does not hinderdriver's vision during driving the automobile 9700. Thus, the displaydevice or input/output device of one embodiment of the present inventioncan be provided in the windshield of the automobile 9700. Note that inthe case where a transistor or the like for driving the display deviceor input/output device is provided in the display device or input/outputdevice, a transistor having a light-transmitting property, such as anorganic transistor using an organic semiconductor material or atransistor using an oxide semiconductor, is preferably used.

The display portion 9712 is a display device provided on a pillarportion. For example, an image taken by an imaging unit provided in thecar body is displayed on the display portion 9712, whereby the viewhindered by the pillar portion can be compensated. The display portion9713 is a display device provided on the dashboard. For example, animage taken by an imaging unit provided in the car body is displayed onthe display portion 9713, whereby the view hindered by the dashboard canbe compensated. That is, by displaying an image taken by an imaging unitprovided on the outside of the automobile, blind areas can be eliminatedand safety can be increased. Displaying an image to compensate for thearea which a driver cannot see, makes it possible for the driver toconfirm safety easily and comfortably.

FIG. 51D illustrates the inside of a car in which bench seats are usedfor a driver seat and a front passenger seat. A display portion 9721 isa display device provided in a door portion. For example, an image takenby an imaging unit provided in the car body is displayed on the displayportion 9721, whereby the view hindered by the door can be compensated.A display portion 9722 is a display device provided in a steering wheel.A display portion 9723 is a display device provided in the middle of aseating face of the bench seat. Note that the display device can be usedas a seat heater by providing the display device on the seating face orbackrest and by using heat generation of the display device as a heatsource.

The display portion 9714, the display portion 9715, and the displayportion 9722 can provide a variety of kinds of information such asnavigation data, a speedometer, a tachometer, a mileage, a fuel meter, agearshift indicator, and air-condition setting. The content, layout, orthe like of the display on the display portions can be changed freely bya user as appropriate. The information listed above can also bedisplayed on the display portions 9710 to 9713, 9721, and 9723. Thedisplay portions 9710 to 9715 and 9721 to 9723 can also be used aslighting devices. The display portions 9710 to 9715 and 9721 to 9723 canalso be used as heating devices.

A display portion including the display device of one embodiment of thepresent invention can be flat, in which case the display device does notnecessarily have a curved surface or flexibility.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Example 1

In this example, Ca tests were conducted to evaluate a moisture barrierproperty of the protection film 23 of one embodiment of the presentinvention. The results are described.

A sample was fabricated in the following manner: an 80-nm-thick calciumfilm was formed on a glass substrate by vacuum evaporation; an adhesivefor one drop fill (ODF) was applied thereon; the glass substrate wasbonded to another glass substrate in a vacuum; the adhesive was cured;and then, the protection film 23 was formed. The width of the bondedportion between the glass substrates was approximately 1 mm.

As the protection film 23, an aluminum oxide film was formed by an ALDmethod. A 100-nm-thick aluminum oxide film was formed by a thermal ALDmethod using trimethyl aluminum (TMA) and ozone as precursors.

FIG. 52 shows the results of the Ca tests of samples with/without theprotection film formed by an ALD method. The horizontal axis representsthe preservation time at 60° C. and at a humidity of 90%, and thevertical axis represents light transmittance. A high light transmittancemeans a large amount of moisture.

According to FIG. 52, in the case of samples without the protection film23, the light transmittance tends to increase because moisture entersthe samples. In contrast, in the case of the sample with the protectionfilm 23 of one embodiment of the present invention which is formed by anALD method, a change in light transmittance was not observed. Therefore,one embodiment of the present invention has an effect of suppressingentry of moisture.

Example 2

In this example, voltage holding characteristics of a test cell in whichliquid crystal was sealed and the protection film 23 of one embodimentof the present invention was provided was evaluated. The results aredescribed.

Table 1 lists the specifications of the test cells, and Table 2 listsmeasurement conditions.

TABLE 1 Electrode area 29 mm × 29 mm Cell gap 4 μm Alignment treatmentTwist rubbing Liquid crystal (two kinds)

 ε = 3.8,  

 n = 0.1102

 ε = −3.0,  

 n = 0.0998 Sealed width approx. 1 mm AlOx film thickness approx. 70 nm,110 nm

TABLE 2 Measurement System Model 6254 (TOYO Corporation) Soak Voltage ±5 V Soak time   4 msec Holding time 9996 msec Temperature   30° C.

Each of the test cells has a structure in which liquid crystal issandwiched between electrodes having a light-transmitting property (ITOelectrodes), and was fabricated by an ODF process. Then, an aluminumoxide film was formed as the protection film 23. The aluminum oxide filmwas formed at 80° C. by a thermal ALD method using TMA and ozone asprecursors. Two types of the aluminum oxide films (thickness: 70 nm, 110nm) were prepared. For the evaluation, positive-type liquid crystal andnegative-type liquid crystal were used.

FIG. 53 shows measurement results of voltage holding ratios of samplesin which the protection film 23 of one embodiment of the presentinvention and positive-type liquid crystal are used. FIG. 54 showsmeasurement results of voltage holding ratios of samples in which theprotection film 23 of one embodiment of the present invention andnegative-type liquid crystal are used. The horizontal axis representsthe preservation time at 60° C. and at a humidity of 90%, and thevertical axis represents the voltage holding ratios.

According to FIG. 53 and FIG. 54, it is found that in the samples usingpositive-type liquid crystal and the samples using negative-type liquidcrystal, the voltage holding ratios are not changed from the startperiod, that is, long-term reliability of a voltage holding ratio isimproved. This is because the samples include the protection film 23 ofone embodiment of the present invention. This effect can be obtained inboth cases where the thickness of the protection film 23 is 70 nm and110 nm Therefore, the protection film 23 of one embodiment of thepresent invention enables more stable voltage holding, so that operationreliability can be improved even at driving with reduced writingoperations.

Example 3

In this example, a display device including the liquid crystal elementof one embodiment of the present invention was manufactured. The displayresult of the display device is described.

Table 3 lists specifications of the display device including the liquidcrystal element. The display device is a high-definition liquid crystalpanel.

TABLE 3 Screen 4.29 inch Diagonal Resolution 1080 × RGB (H) × 1920 (V):Full-HD Pixel Pitch 49.5 μm (H) × 49.5 μm (V) Pixel Density  513 ppi FETCAAC-OS Scan driver Integrated Bezel   <1 mm

In the display device, an aluminum oxide film was formed as theprotection film 23 by an ALD method. An aluminum oxide film was formedto a thickness of approximately 100 nm at 80° C. by a thermal ALD methodusing trimethyl aluminum (TMA) and ozone as precursors.

FIG. 55 shows display of the display device for which one embodiment ofthe present invention is used. The frame width is less than or equal to1 mm According to FIG. 55, it is found that by sealing the side surfaceportion and the peripheral portion with the protection film 23 formed byan ALD method, a display device which has high display quality and ishighly reliable while having a narrow frame width can be provided.

Example 4

In this example, a side surface portion of the display panel 20, whichwas used in Example 3, was subjected to cross-sectional observation witha scanning electron microscope (SEM) and element mapping analysis withan energy dispersive X-ray spectroscopy (EDX). The results of theobservation and the analysis are described.

For the SEM observation, SU8030 produced by Hitachi High-TechnologiesCorporation was used. For the EDX analysis, EMAXEvolution produced byHORIBA, Ltd. was used. The side surface portions of the substrates werefixed to a resin 378, and then observation was performed. FIG. 56A is aschematic cross-sectional view of the observed display panel 20. Foreasier describing, regions in which a transistor, a capacitor, aninsulating layer, a conductive layer, and the like are formed areillustrated as a region 15 and a region 16. An observed region is aregion 17 in FIG. 56A. FIG. 56B is a schematic view of the region 17.The region 17 includes the substrate 100, the substrate 300, theinsulating layer 131, the insulating layer 180, the protection film 23,the insulating layer 330, the conductive layer 380, the bonding layer370, and the resin 378.

FIG. 57A is a cross-sectional SEM image of the region 17. FIG. 57B showsEDX analysis results of aluminum mapping. FIG. 57C shows EDX analysisresults of oxygen mapping.

FIG. 57A indicates that the region 17 includes the substrate 100, theinsulating layer 131, the insulating layer 180, the bonding layer 370,the resin 378, and the conductive layer 380. According to FIGS. 57B and57C, it is found that in the side surface portion of the display device,aluminum and oxygen are detected along the conductive layer 380, thebonding layer 370, and the insulating layer 180; thus, the aluminumoxide film, which is the protection film 23 formed by an ALD method, isuniformly formed.

An upper portion and a lower portion of the region 17 were enlarged andsubjected to cross-sectional SEM observation. The upper portion wasfurther subjected to EDX analysis. FIG. 58A is a SEM image of the upperportion of the region 17. FIG. 58B shows the EDX analysis result ofaluminum mapping in the upper portion of the region 17. FIG. 58C shows aresult of cross-sectional SEM observation in the lower portion of theregion 17.

In FIGS. 58A and 58B, existence of aluminum is confirmed in addition tothe existence of the insulating layer 330, the bonding layer 370, theresin 378, and the conductive layer 380, and an aluminum oxide film thatfunctions as the protection film 23 is uniformly formed with respect toside surface portions, which include the bonding layer 370, theconductive layer 380, and the like, of the display device. Moreover,FIG. 58C shows that the aluminum oxide film that functions as theprotection film 23 is also uniformly formed in the lower portion.

As described above, each of the structures shown in FIGS. 57A to 57C andFIGS. 58A to 58C reflects the structure illustrated in FIG. 56B; thus,it was verified that the present invention can be implemented. Thedisplay device to which one embodiment of the present invention is usedcan have a high barrier property, and can have an improved reliabilityeven when the frame width is narrowed.

Example 5

In this example, the concentration of impurities in the protection film23 was measured, and the results are described.

The impurity concentration was measured by secondary ion massspectrometry (SIMS). A dynamic SIMS apparatus PHI ADEPT-1010 produced byULVAC-PHI, Inc. was used as an analysis apparatus. The samples foranalysis were prepared in the following manner a thermal oxidation filmwas formed on a silicon wafer by oxidation with a hydrochloric acid, andthen an aluminum oxide (AlOx) film was formed by an ALD method or analuminum oxide film was formed by a sputtering method as the protectionfilm 23 over the thermal oxidation film.

FIG. 59 shows SIMS analysis results of hydrogen, carbon, and fluorine inthe aluminum oxide film.

FIG. 59 shows that the aluminum oxide film formed by an ALD method has ahydrogen concentration of approximately 1×10²¹ atoms/cm³, a carbonconcentration of approximately 1×10²⁰ atoms/cm³, and a fluorineconcentration of approximately 1×10²⁰ atoms/cm³. These elementconcentrations are different from those of the aluminum oxide filmformed by a sputtering method; thus, the difference is due to a filmformation method. In addition, the impurity concentration of thealuminum oxide film formed by an ALD method can be further reduced,which can improve the reliability of a display device.

Example 6

In this example, the light transmittances of the samples were measuredafter the preservation test at high temperature and high humidity, andthe measurement results are described.

Some samples which include an aluminum oxide film formed by an ALDmethod and some samples which do not include the aluminum oxide filmwere prepared.

These samples have the same specifications as the liquid crystal displaydescribed in Example 3. These samples were subjected to a preservationtest at a high temperature of 60° C. and a high humidity of 90% and thento idling stop (IDS) driving at a frame frequency of 0.1 Hz, and theirlight transmittances were measured. The measuring point was set to 5 mminner than the edge of each sample (FIG. 60A). For the measurement,halftone display was performed because a change in light transmittancecaused by writing is most easily observed in halftone (gray) display(see FIG. 61).

Note that idling stop (IDS) driving is a driving method in which datarewriting is stopped after data writing is executed. Although theconventional driving method needs approximately 60-time rewritingoperations per second as shown in FIG. 60B, the IDS driving can reducethe number of rewriting operations as shown in FIG. 60C and thus can cutpower consumption.

FIGS. 62A and 62B show the light transmittance measurement results ofsamples subjected to the preservation test at a temperature of 60° C.and a humidity of 90% over time. Note that in FIGS. 62A and 62B, achange in light transmittance is converted into a change in gray level.The change in gray level caused by writing was approximately 4 levels inthe samples which include the aluminum oxide film (FIG. 62A). Incontrast, the change in gray level was as large as approximately 13levels in the samples which do not include the aluminum oxide film (FIG.62B).

Therefore, use of one embodiment of the present invention can reduce thechange in gray level and thus can improve long-term reliability of aliquid crystal display.

Example 7

In this example, described are the evaluation results of oxide aluminumfilms which were deposited at different temperatures by an ALD method.

<Density of Oxide Aluminum Film>

Samples for measuring the density of aluminum oxide films were formed bydepositing oxide aluminum over Si wafers to a thickness of 100 nm by anALD method. The deposition temperatures of the oxide aluminum films were80° C., 100° C., and 120° C. The same precursors used in Example 3 wereused.

The density of the aluminum oxide films was measured by X-rayreflectometry with TRXV-SMX produced by TECHNOS CORP.

FIG. 63 shows the density of the aluminum oxide films deposited atdifferent temperatures. FIG. 63 indicates that the higher the depositiontemperature is, the higher the density tends to be.

<Moisture Permeability of Aluminum Oxide Films>

The aluminum oxide films deposited by the above-described method weresubjected to the same Ca test conducted in Example 1. FIG. 64 shows theresults. The horizontal axis represents time of a test at a temperatureof 60° C. and a humidity of 90% and the vertical axis represents lighttransmittance. A higher light transmittance means more water enters thefilm.

From FIG. 64, it is found that the samples formed at depositiontemperatures of 80° C. and 100° C. can keep low light transmittance.Furthermore, the sample formed at a deposition temperature of 100° C. islikely to obtain low light transmittance stably. This is because thealuminum oxide film that functions as a protection film preventsmoisture from entering.

Accordingly, with one embodiment of the present invention, a highlyreliable display device can be provided.

This application is based on Japanese Patent Application serial no.2014-238566 filed with Japan Patent Office on Nov. 26, 2014, JapanesePatent Application serial no. 2014-243313 filed with Japan Patent Officeon Dec. 1, 2014, Japanese Patent Application serial no. 2015-044820filed with Japan Patent Office on Mar. 6, 2015, Japanese PatentApplication serial no. 2015-109045 filed with Japan Patent Office on May28, 2015, the entire contents of which are hereby incorporated byreference.

What is claimed is:
 1. A display device comprising: a first substrate; asecond substrate; a first insulating layer on a first plane of the firstsubstrate; a second insulating layer on a first plane of the secondsubstrate; a bonding layer between the first insulating layer and thesecond insulating layer; and a protection film in contact with the firstsubstrate, the first insulating layer, the bonding layer, the secondinsulating layer, and the second substrate, wherein an area of the firstplane of the first substrate is the same as an area of the first planeof the second substrate, and wherein the first plane of the firstsubstrate and the first plane of the second substrate face each other.2. The display device according to claim 1, further comprising atransistor, a capacitor, a display element, a light-blocking layer, acoloring layer, and a spacer between the first plane of the firstsubstrate and the first plane of the second substrate.
 3. The displaydevice according to claim 1, wherein the protection film comprises anyone of oxygen, nitrogen, and a metal.
 4. The display device according toclaim 1, wherein the protection film comprises any one of aluminumoxide, hafnium oxide, zirconium oxide, titanium oxide, zinc oxide,indium oxide, tin oxide, indium tin oxide, tantalum oxide, siliconoxide, manganese oxide, nickel oxide, erbium oxide, cobalt oxide,tellurium oxide, barium titanate, titanium nitride, tantalum nitride,aluminum nitride, tungsten nitride, cobalt nitride, silicon nitride,manganese nitride, hafnium nitride, ruthenium, platinum, nickel, cobalt,manganese, and copper.
 5. The display device according to claim 1,wherein the protection film comprises any one of fluorine, carbon, andhydrogen.
 6. The display device according to claim 1, wherein aconcentration of fluorine in the protection film is greater than orequal to 1×10¹⁸ atoms/cm³ and less than 1×10²² atoms/cm³.
 7. The displaydevice according to claim 1, wherein a concentration of carbon in theprotection film is greater than or equal to 1×10¹⁷ atoms/cm³ and lessthan 1×10²² atoms/cm³.
 8. The display device according to claim 1,wherein a concentration of hydrogen in the protection film is greaterthan or equal to 1×10¹⁹ atoms/cm³ and less than 1×10²² atoms/cm³.
 9. Thedisplay device according to claim 2, wherein the display element is aliquid crystal element.
 10. The display device according to claim 2,wherein the display element is an organic EL element.
 11. An electronicdevice comprising the display device according to claim 1, the displaydevice comprising a microphone and a speaker.
 12. A display devicecomprising: a first substrate; a second substrate; a first insulatinglayer on a first plane of the first substrate; a second insulating layeron a first plane of the second substrate; a bonding layer between thefirst insulating layer and the second insulating layer; and a protectionfilm in contact with the first substrate, the first insulating layer,the bonding layer, the second insulating layer, and the secondsubstrate, wherein an area of the first plane of the second substrate issmaller than an area of the first plane of the first substrate, andwherein the first plane of the first substrate and the first plane ofthe second substrate face each other.
 13. The display device accordingto claim 12, further comprising a transistor, a capacitor, a displayelement, a light-blocking layer, a coloring layer, and a spacer betweenthe first plane of the first substrate and the first plane of the secondsubstrate.
 14. The display device according to claim 12, wherein theprotection film comprises any one of oxygen, nitrogen, and a metal. 15.The display device according to claim 12, wherein the protection filmcomprises any one of aluminum oxide, hafnium oxide, zirconium oxide,titanium oxide, zinc oxide, indium oxide, tin oxide, indium tin oxide,tantalum oxide, silicon oxide, manganese oxide, nickel oxide, erbiumoxide, cobalt oxide, tellurium oxide, barium titanate, titanium nitride,tantalum nitride, aluminum nitride, tungsten nitride, cobalt nitride,silicon nitride, manganese nitride, hafnium nitride, ruthenium,platinum, nickel, cobalt, manganese, and copper.
 16. The display deviceaccording to claim 12, wherein the protection film comprises any one offluorine, carbon, and hydrogen.
 17. The display device according toclaim 12, wherein a concentration of fluorine in the protection film isgreater than or equal to 1×10¹⁸ atoms/cm³ and less than 1×10²²atoms/cm³.
 18. The display device according to claim 12, wherein aconcentration of carbon in the protection film is greater than or equalto 1×10¹⁷ atoms/cm³ and less than 1×10²² atoms/cm³.
 19. The displaydevice according to claim 12, wherein a concentration of hydrogen in theprotection film is greater than or equal to 1×10¹⁹ atoms/cm³ and lessthan 1×10²² atoms/cm³.
 20. The display device according to claim 13,wherein the display element is a liquid crystal element.
 21. The displaydevice according to claim 13, wherein the display element is an organicEL element.
 22. An electronic device comprising the display deviceaccording to claim 12, the display device comprising a microphone and aspeaker.